2018 Solved Old Paper (BOT-102)

Ans.

Pseudopodium:-

> In Sphagnum sporogonium is elevated on a short cylindrical, leafless stalk, the pseudopodium.

> The pseudopodium is gametophytic and it is formed by the post fertilization intercalary growth of the axis of the archegonial branch.

> The pseudopodium together with the basal portion of the calyptra forms a sac-like structure encloses the foot. 

> The main functions of the pseudopodium are to elevate the capsule for above the perichaetial leaves, to compensate the suppression of seta and to help in the dispersal of spores.

Ans.

Exoscopic embryogeny:- It can be defined when the two cells the developed after the first division of the egg cell. The outer part gives rise to the embryo and the inner part form the foot. It is seen in the Brophyta etc.

Ans.

Apogamy:- When the embryo develops from the antipodal cell or the synergid, it is called apogamy. As shown in the diagram below. Example:- Onion

Ans.

Eusporangium versus Leptosporangium:-

Eusporangium is developed from a group of initial cells while Leptosporangium is developed from a single initial cell while  

Ans.

Ligule:- The ligule is specialized for the production and secretion of extracellular mucilage. The ligule is a structure on the adaxial surface of the microphylls and sporophylls of Selaginella and consists of apical, basal, glossopodial, and sheath cells.

Ans.

Glochidia:- Microspores of Azolla and Salvinia do not normally occur singly, but rather are confined within a bubbly, gelatinous substance, the massula, which distally may have numerous hooked structures termed glochidia, which serve to attach the massula to the megaspore. The massulae are invested on the surface by hair-like appendages with sagittate tips known as glochidia.

Ans.

Classification of Bryophytes (ब्रायोफाइट्स का वर्गीकरण):- According to the newest classification, Bryophyta is split into three classes:

(नवीनतम वर्गीकरण के अनुसार, ब्रायोफाइटा को तीन वर्गों में विभाजित किया गया है:)

1. Hepaticopsida (Liverworts) 

2 Anthocerotopsida (Hornworts)

3. Bryopsida (Mosses)

1. Hepaticopsida (Liverworts):- 

> The name hepaticopsida comes from the word “hepatic” which means liver. 

(हिपेटिकोप्सिडा नाम "हिपेटिक" शब्द से आया है जिसका अर्थ है यकृत।)

> The most basic bryophytes are liverworts. 

(सबसे आधारभूत ब्रायोफाइट्स लिवरवॉर्ट्स हैं।)

> They prefer moist rocks and wet soil to live in. 

(वे रहने के लिए नम चट्टानें और गीली मिट्टी पसंद करते हैं।)

> Because they dwell near water, their chances of drying are much reduced. 

(क्योंकि वे जल के पास रहते हैं, उनके सूखने की संभावना बहुत कम हो जाती है।)

> The gametophyte plant is either thalloid or foliose.

(युग्मकोदभिद पौधा या तो थैलॉइड या पत्तेदार होता है।)

> Thalloid forms are dorsiventral, lobed, and dichotomously branched.

(थैलॉइड रूप पृष्ठाधरी, पालित और द्विभाजित शाखा वाले होते हैं।)

> Rhizoids are unicellular, unbranched and of 2 type:

(मूलाभास एककोशिकीय, अशाखित और 2 प्रकार के होते हैं:)

> Sex organs are borne dorsally embedded in gametophytic tissues.

(लैंगिक अंग युग्मकोदभिद ऊतकों में पृष्ठीय रूप से धँसे होते हैं।)

> The sporophyte is a compilation of only capsule (in Riccia) or foot, seta, and capsule (in Marchantia).

The columella is absent in the capsule.

(बीजाणुदभिद केवल कैप्सूल (रिक्सिया में) या फुट, सीटा और कैप्सूल (मार्केन्शिया में) का संकलन है। कैप्सूल में कोल्यूमेला अनुपस्थित होता है।)

> Sporogenous tissues develop from endothecium.

(बीजाणुजनित ऊतक एन्डोथेसियम से विकसित होते हैं।)

> Hepaticopsida is further divided into 5 orders:

(हेपेटिकॉप्सिडा को आगे 5 गणों में विभाजित किया गया है:)

a. Sphaerocarpales:- 2 families: (2 कुल)

i. Sphaerocarpaceae:- Eg.- Sphaerocarpos, Geothallus

ii. Riellaceae:- Eg.- Riella

b. Marchantiales:- 4 families: (4 कुल)

i. Ricciaceae:- Eg.- Riccia, Ricciocarpus, Tesselina (Oxymitra)

ii. Targionaceae:- Eg.- Targionia, Cyathodium, Aitchisoniella

iii. Monocleaceae:- Eg.- Monoclea

iv. Marchantiaceae:- Eg.- Marchantia, Plagiochasma, Dumortiera, Lunularia, Reboulia, Grimaldia, Monoselenium

c. Jungermanniales:- 3 families: (3 कुल)

i. Ricardiaceae (Aneuraceae):- Eg.- Ricardia (Aneura)

ii. Blyttiaceae (Pallavaciniaceae):- Eg.- Blyttia

iii. Codoniaceae:- Eg.- Pellia, Petalophyllum, Fossombronia

d. Calobryales:- 1 family: (1 कुल)

i. Calobryaceae:- Eg.- Calobryum, Haplomitrium

e. Takakiales:- 1 family: (1 कुल)

i. Takakiaceae:- Eg.- Takakia

2. Anthocerotopsida (Hornworts):-

> They are commonly known as hornworts.

(इन्हें आमतौर पर हॉर्नवॉर्ट्स के नाम से जाना जाता है।) 

> The gametophytic body is flat, dorsiventral, simple thalloid, and has no internal differentiation.

(युग्मकोदभिद शरीर चपटा, पृष्ठीय, सरल थैलॉइड होता है और इसमें कोई आंतरिक विभेदन नहीं होता है।)

> Rhizoids are unicellular, unbranched and smooth-walled.

(मूलाभास एककोशिकीय, अशाखित और चिकनी भित्ति वाले होते हैं।)

> Each cell has one chloroplast with a pyrenoid.

(प्रत्येक कोशिका में पाइरेनॉइड के साथ एक क्लोरोप्लास्ट होता है।)

> Sex organs are present dorsally embedded in the thallus.

(लैंगिक अंग थैलस में पृष्ठीय रूप से धँसे होते हैं।)

> Sporogenous tissues develop from amphithecium.

(बीजाणुजनित ऊतक एम्फ़िथेशियम से विकसित होते हैं।)

> Pseudoelaters are present in the capsule.

(कैप्सूल में कूटइलेटर्स पाये जाते हैं।)

> The columella is present within the capsule, which originates from the endothecium.

(कोल्यूमेला कैप्सूल के भीतर मौजूद होता है, जो एंडोथेसियम से उत्पन्न होता है।)

> It has only one order:

(इसका केवल एक ही गण है:)

a. Anthocerotales:- 2 families: (2 कुल)

i. Anthocerotaceae:- Eg.- Anthoceros, Paeoceros, Dendroceros, Megaceros

ii. Notothylaceae:- Eg.- Notothylas

3. Bryopsida (Mosses):-

> They are commonly called mosses.  

(इन्हें आम तौर पर मौस कहा जाता है।)

> The gametophyte is divided into protonema and foliose gametophore.

(युग्मकोदभिद को प्रोटोनिमा और पर्णीय गैमेटोफोर में विभाजित किया गया है।)

> Foliose gametophore is formed of the stem as an axis and leaves without a midrib.

(पर्णीय गैमेटोफोर एक अक्ष के रूप में तने और मध्यशिरा रहित पत्तियों से बना होता है।)

> Rhizoids are multicellular with oblique septate.

(मूलाभास तिरछे पट्ट युक्त बहुकोशिकीय होते हैं।)

> Sex organs are borne apically on the stem.

(लैंगिक अंग शीर्षस्थ रूप से तने पर उत्पन्न होते हैं।)

> Elaters are absent.

(इलेटर अनुपस्थित होते हैं।)

> The sporophyte is differentiated into foot, seta and capsule.

(बीजाणुदभिद को फुट, सीटा और कैप्सूल में विभेदित किया जाता है।)

> Sporogenous tissues develop from endothecium.

(बीजाणुजनित ऊतक एन्डोथेसियम से विकसित होता है।)

> The columella is present.

(कोल्यूमेला उपस्थित होता है।)

> Separation of the lid is the result of the Dehiscence of the capsule.

(ढक्कन का अलग होना कैप्सूल के फूटने का परिणाम है।)

> Bryopsida is further divided into 3 sub-classes:

(ब्रायोप्सिडा को आगे 3 उप-वर्गों में विभाजित किया गया है:)

a. Sphagnidae:- 1 order: (1 गण)

I. Sphagnales:- 1 family: (1 कुल)

i. Sphagnaceae:- Eg.- Sphagnum

b. Andreidae:- 1 order: (1 गण)

I. Andreales:- 1 family (1 कुल)

i. Andreaceae:- Eg.- Andrea (Granite moss)

c. Eubryidae (Bryidae):- 3 orders: (3 गण)

I. Polytrichales:- 1 family: (1 कुल)

i. Polytrichaceae:- Eg.- Polytrichum, Pogonatum, Atrichium, Oligotrichum, Lyellia

II. Funariales:- 5 families (5 कुल)

i. Gigaspermaceae

ii. Funariaceae:- Eg.- Funaria

iii. Disceliaceae

iv. Oedipodiaceae

v. Splachaceae

III. Buxbaumiales:- 1 family:

i. Buxbaumiaceae:- Eg.- Buxbaumia, Diphyscium

Ans.

Sexual reproduction (लैंगिक जनन):- 

> Marchantia is heterothallic i.e.,dioecious. In female plant, the archegonia are borne on special erect, stalked branch called archegoniophore. Similarly in male plants the antheridia are borne on erect, stalked branch called antheridiophore.

(Marchantia विषमथैलिक अर्थात एकलिंगाश्रयी होता है। मादा पौधे में स्त्रीधानियाँ विशेष सीधी, वृंतीय शाखा पर उत्पन्न होते हैं जिसे स्त्रीधानीधर कहा जाता है। इसी प्रकार नर पौधों में पुंधानियाँ सीधी, वृंतीय शाखा पर उत्पन्न होते हैं जिसे पुंधानीधर कहा जाता है।)

i. Antheridiophore (पुंधानीधर):-

- Each antheridiophore is similar in position to the archegoniophore. 

(प्रत्येक पुंधानीधर की स्थिति स्त्रीधानीधर के समान होती है।)

- It consists of a stalk (1-3 cm long) bearing at its apex a disc with generally 8-lobed margin. 

[इसमें एक वृंत (1-3 सेमी लंबा) होता है जिसके शीर्ष पर आम तौर पर 8 - पालियों वाले किनारे वाली एक डिस्क होती है।]

- Towards the upper part of the disc antheridia occur in flask shaped cavities.

(डिस्क के ऊपरी भाग की ओर पुंधानियाँ फ्लास्क के आकार की गुहाओं में होती हैं।)

- Each mature antheridium is a pear-shaped or globular body with a short stalk, and a jacket layer of single layer of thin walled cells. 

(प्रत्येक परिपक्व पुंधानी एक नाशपाती के आकार का या गोलाकार काय होता है जिसमें एक छोटा वृंत होटा है, और इसके जैकेट में पतली भित्ति वाली कोशिकाओं की एकल परत होती है।)

- Within the antheridial jacket lie numerous androcyte mother cells. 

(पुंधानी जैकेट के भीतर असंख्य एंड्रोसाइट मातृ कोशिकाएं होती हैं।)

- Each androcyte mother cell divides diagonally to form two triangular androcytes (antherozoid mother cells). Ultimately, each androcyte is metamorphosed into biflagellate sperm i.e., antherozoid.

[प्रत्येक एंड्रोसाइट मातृ कोशिका तिरछे विभाजित होकर दो त्रिकोणीय एंड्रोसाइट्स (पुमणु मातृ कोशिकाएं) बनाती है। अंततः, प्रत्येक एंड्रोसाइट द्विकशाभिकीय शुक्राणु अर्थात पुमणुओं में रूपांतरित हो जाता है।]

- Development of Antheridium (पुंधानी का विकास):-

ii. Archegoniophore (स्त्रीधानीधर):-

- Each archegoniophore arises from a region just behind the apex of the thallus. 

(प्रत्येक स्त्रीधानीधर थैलस के शीर्ष के ठीक पीछे के क्षेत्र से उत्पन्न होता है।)

- The mature archegoniophore consists of a long stalk bearing at its apex a distinct, generally 8-rayed or lobed stellate disc. 

(परिपक्व स्त्रीधानीधर में एक लंबा वृंत होता है जिसके शीर्ष पर एक विशिष्ट, आम तौर पर 8-किरण वाली या पालि वाली तारकीय डिस्क होती है।)

- Between the rays, group of archegonia are arranged in radial rows,each row being borne in an inverted position.

(किरणों के बीच, स्त्रीधानियों के समूह को अरीय पंक्तियों में व्यवस्थित किया जाता है, प्रत्येक पंक्ति एक उलटी स्थिति में होती है।)

- Each archegonium is a flask shaped structure and consists of an arrow neck with several neck canal cells and a swollen venter containing a ventral canal cell and an egg. 

(प्रत्येक स्त्रीधानी एक फ्लास्क के आकार की संरचना होती है और इसमें एक तीर ग्रीवा होती है जिसमें कई ग्रीवा नाल कोशिकाएं होती हैं और एक फूला हुआ अंडधा होता है जिसमें एक अंडधा नाल कोशिका और एक अंडा होता है।)

- Each archegonium is attached by a short stalk to the lobe of the disc.

(प्रत्येक स्त्रीधानी एक छोटे वृंत द्वारा डिस्क की पालि से जुड़ी होती है।)

- Development of Archegonium (स्त्रीधानी का विकास):-

Ans.

Ecological Role of Bryophytes:-

a. Bryophytes as Pioneer of Vegetation

b. Role of Bryophytes in Soil Erosion

a. Bryophytes as Pioneer of Vegetation:-

> Many bryophytes are the first ones to appear on open and often nutrient-poor sites where no other plant is able to grow. For instance, they grow on bare rocks and on recently deposited volcanic ash. 

> Gradually, the bryophytes build up an organic layer that is invaded by microorganisms, resulting in changes in the mineral substratum beneath. This increases in nutrient availability makes the site suitable for invasion by vascular plants. 

> In this way, bryophytes help in succession of plants on bare rocks by becoming pioneer plant community (pioneers-first to appear). 

> Several bryophytes like Andreaea are restricted mainly to bare rock surfaces. Most of these bryophytes are highly tolerant to extended period of desiccation.

> The mosses are also pioneer species on burnt sites. Every year large areas of grassland, and temperate and tropical forests catch fire. The resulting tracts of land provide habitats for the succession of mosses like Funaria and Polytrichum.

> Mosses are pioneers in dune systems as well. They help in retaining moisture and stabilizing dunes that otherwise are at the mercy of the wind. Eg. Ceratodon and Tortula.

b. Role of Bryophytes in Soil Erosion:-

> You have learnt that bryophytes grow as cdmpact cushions forming a carpet on the forest floor. 

> Actually, their rhizoids bind soil particles together and also interweave with the rhizoids of adjacent plants keeping the whole cushion compact and difficult to detach from the soil. The soil particles thus trapped do not flow alongwith water during floods.

> The colonization of bryophytes on the roadside is important in stabilizing these sites.

> Species of Barbula, Weissia, and Bryum are pioneers on new road banks.

> Extensive sand dune systems occur along many sea coasts of the world. 

> Mosses play a very important role in helping to retain moisture and stabilize dunes. Such mosses can survive even if they get covered by sand. An example of such a moss is Cerafodonpurpureus.

> Mosses have a potential role as inhibitors of soil erosion due to their trample-resistant structure and their high regenerative ability.

> In present times, certain mosses like Polytrichum, Atrichum and Ceratodon are grown to prevent soil erosion around fruit trees such as apples and pears.

Ans.

Soral evolution:-

Sorus:- It is brownish or yellowish cluster of spore-producing structures (sporangia) usually located on the lower surface of fern leaves. A sorus may be protected during development by a scale or flap of tissue called an indusium.

Types of sorus:-

i. Simple sorus:-

> The Simplices are primitive and extend to the Paleozoic. 

> All sporangia within a sorus may be at the same stage of development (Simplices).

> The sporangia in such a sorus development simultaneously and all of them mature together. 

> Eg.- Ophioglossum and Osmunda.

ii. Gradate sorus:-

> In such cases the internal space within the radial sorus gets filled by overlapping sporangia. 

> Overcrowding results and there is no space for the proper dehiscence of sporangia and consequently some of them do not dehisce. 

> The Gradate with an oblique annulus, occupy a middle position and have been discovered in the Mesozoic. 

> Eg.- Dicksonia, Loxosoma, Trichomanes, Cyathea, Alsophila etc.

iii. Mixed sorus:-

> The spores are released in a staggered fashion and even if the environmental conditions are not favorable when the spores are initially released; this problem is solved by a constant crop of spores over a given length of time. 

> Mixtae annulus is present but in a vertical fashion. 

> Eg.- Polypodiaceae (Adiantum, Pteris, Pteridium, Davallia) Polypodiaceae

Indusial protection:- The indusium may be formed as an epidermal outgrowth covering receptacle and sporangia (true indusium) or it may merely be the in turning of the margin of the leaf to protect the sporangia (pseudo indusium or false indusium).

Position of sorus in ferns:- The Ophioglossales are group of interesting ferns in which the sporangia are marginal in position. 

> In Maeattia, Angiopteris, Danaea etc. the sori are elongagated and are situated below the lateral veins. 

> In christensia the sori are naked, circular and are irregular arranged between the lateral veins. 

> In Adiantum the sporangia develop on the underside of special marginal flaps of lamina that become reflexed and protect the sorus 

> The sori in Mattoniaceae are ventral in position and are usually arranged in two rows on either side of the midrib. 

> In Glecheniaceae, the sporangia from distinct sori on the ventral surface of the leaves. 

> The sporangia in Osmunda, Davalia, Trivhomanes and many other ferns are also marginal in position.

> In Marsileales and the Salviniales the sporangia develop in sori that are borne within distinct structure called the Sporocarp.

- In Salviniales the smaller sporocarp contain many microsporangia each and the larger ones contain one or more megasporangia per sporocarp. 

- The sporocarp in Marsilea enclose sori that contain both micro and megasporongia. 

Ans.

Study of sporophyte:-

> Each plant consists of an aerial portion and a rhizome, or subterranean region, but has no roots. 

> The plant possesses no true leaves, what appear to be leaves are flattened stems. 

> The fronds emerge directly from the fibrous root-mats which clad the trunks of mature tree ferns such as Dicksonia and Cyathea.

> Aerial part varied from 3 to 8 inches in length.

Ans.

Sporocarp of Salvinia:- 

- The sporocraps appear in clusters ranging in number from 4 to 20. 

- The sporocarps are usually borne on the inner segments of submerged leaves. 

- In arrangement, the sporocarps are sympodial.

- The shape of the sporocarp varies from globose to ovoid, occasionally flattened also with ridged surfaces. 

- The wall of the sporocarp is made up of two layers of cells. The outermost layer when young is clad with hairs.

- Externally all sporocarps are alike. The sporocarps are always bisporangiate. 

- Each sporocarp contain many sori.

- The sporocarp at its base has a stout columnar receptacle which carries the vascular supply into the sporocarp. 

- The receptacle is un-branched in the sporocarps of S. natans.

> Internal structure of sporocarp:-

- A sectional view of mature sporocarp shows a well-developed wall enclosing the, sporangia. 

- Each sprocarp has 4 valves.

> Sporangia:- 

i. Microspoangia:-

- The micro-sporangium consists of a short stalk and a generally ovoid capsule. 

- Enclosed in the sporangium are 16 microspore mother cells and consequently 64 microspores are formed. 

- All the spores attain maturity and survive. 

- The microspores are embedded in the cytoplasmic fluid derived from the tapetum.

- As the spores mature, the tapetal cytoplasm encompassing the spores gets hardened and forms a mass called ‘massula’ or glochidium. 

- The microspores are extremely small, triradiate in appearance and have two wall layers. 

- There is a single nucleus in each microspore.

- Occasionally the number of microspores per microsporangia might vary. In S. auriculata, according to Loyal and Grewal (1966), there are only 8 microspore mother cells and consequently only 32 microspores are formed.

ii. Megasporangia:-

- The mega-sporangium consists of a short stalk and a generally ovoid capsule. 

- The capsule is made up-of a single layer of cells. Internal to the wall of the capsule is a layer of tapetum. 

- Enclosed by the tapetum are found 8 mega-sporocytes which divide meiotically to produce 32 megaspores. Of these spores, all except one degenerate.

Ans.

Sexual reproduction:- 

> Sexual reproduction is oogamous. 

> It takes place by the formation of male and female reproductive organs which develop on special branches. 

> Sphagnum may be monoecious or dioecious. Monoecious species are protandrous (antheridium matures before archegonia).

i. Antheridium:-

- The antheridia or the male sex organs develop on the short lateral branches known as the antheridial

or male branches. 

- These branches develop near the apex of the main shoot of the plant. 

- These branches bear the leaves which are just like the foliage leaves but in comparison they are shorter.

- These leaves are brightly coloured (commonly yellow, purple, brown, bright red or dark green). 

- In the axil of each leaf solitary antheridium develops (antheridsia occur alternately arranged with the

leaves). 

- A mature antheridium consists a long stalk and a globular body.

- When the antheridium is mature, the apical cells of the jacket absorb water, swell and undergo irregular separations which turn backwards. 

> The antherozoids are liberated and swim in water.

- Development of Antheridium:-

ii. The Archegonium:-

- One to five archegonia develop at the tip of the short archegonial branches or female branches. 

- The leaves of the archegonial branches are green and much larger than the vegetative branches. These leaves are called perichaetium. These leaves protect the archegonia, young sporophytes and provide food to the developing sporophytes.

- A mature archegonium is long and stalked structure possessing venter and a long neck enclosing 8 or 9 neck canal cells, a venter canal cell and an egg cell.

- Development of Archegonium:-

> Fertilization:-

- The process of fertilization is similar to other classes of bryophytes. 

- Water is essential for fertilization.

- At the time of fertilization the neck canal cells along with the venter canal cell disintegrate to form a clear passage for the antherozoids. 

- They enter through the cover cells and reach up to the egg, but only one fuses with the egg to form the zygote.

Sporophyte:-

> The sporogonium develops from only one archegonium. 

> The other archegonium, however, may also persist for some time. 

> The mature sporogonium is differentiated into foot and capsule. 

> Both foot and capsule are connected by a short, narrow neck like constriction which represents the suppressed seta, sporogonium is elevated on a short cylindrical, leafless stalk, the pseudopodium.

> The pseudopodium is gametophytic and it is formed by the post fertilization intercalary growth of the axis of the archegonial branch.

> The pseudopodium together with the basal portion of the calyptra forms a sac-like structure encloses the foot. 

> The main functions of the pseudopodium are to elevate the capsule for above the perichaetial leaves, to compensate the suppression of seta and to help in the dispersal of spores.

i. Foot:-

- It is bulbous and made up of parenchymatous cells. 

- The main function is to absorb the food material for the developing sporophyte.

ii. Capsule:-

- It is spherical and dark brown in colour. 

- It contains central columella which is over arched by a done shaped spore sac containing haploid spores . 

- The wall of the capsule is 4-6 layers thick. 

- The outer layer of the capsule wall is called epidermis. 

- The cells of the epidermis are compactly arranged and contain chloroplasts.

- It has many non-functional and rudimentary stomata. 

- In young sporogonium, a circular, convex disc is present at the top of the capsule. It is called operculum. It is separated from the rest of the capsule region by a circular (ring like) groove of thin walled cells called annulus.

> Dispersal of spores or Dehiscence of capsule:-

- On sunny days the columella of mature capsule dries up, breaks down and forms a large air cavity below the air sac. Air enters in this cavity through the rudimentary stomata.

- The pressure of imprisoned air also ruptures the spore sac and the cloud of yellow or orange coloured spores is blown to a height of several centimeters in the atmosphere. The method of spore discharge is,

therefore, known as the air gun or explosive mechanism.

> Structure and Germination of Spore:-

> Each spore is uninucteare, triangular to spherical and has two layered wall with a triradiate mark. 

> The outer wall is ornamented and known as exine while the inner wall is smooth and known as intine. 

> The spores remain viable for few months and germinate under favourable conditions. 

> Spores absorb water and swell up.

> Exine ruptures and intine comes out in the form of a germ tube. 

> The germ tube divides transversely to form 2-4 celled green filaments. It is called primary protonema. > The apical cell loses in activity and some marginal cells of the plate like protonema become active and form secondary protonema with rhizoids and leaf buds. These buds gradually develop into leafy gametophores.

 

Ans.

Evolution of stele:-

Stele:- The central cylinder or core of vascular tissue, consisting of xylem, phloem, pericycle and sometimes medullary rays and pith, is technically called stele. 

Stelar theory:- 

> Van Tieghem and Douliot (1886) developed this theory. 

> They used the term stele in collective sense and mentioned that the stele is not only made up of xylem and phloem, but the tissue like pericycle, vascular rays and pith are also associated with it. 

> According to them the cortex and the stele are the fundamental parts of a shoot and both these parts are separated from each other by the endodermis. 

> According to stellar theory, primarily there is no fundamental difference in the gross anatomy of stem and roots, because in both of them a stele is surrounded by the cortex is present. 

> Foster and Gifford (1959) have mentioned that the most debated and controversial aspect of “stellar theory is the nature of the anatomical boundaries which separate the cortex from the stele”. 

> According to Van Tieghem and Douliot (1886) the endodermis represents the inner boundary of the cortex. The cells of the endodermal layer have the characteristic casparian strip strips. 

> But in the stems of many seed plants, the characteristic endodermal layer is not present. Some have mentioned that in such cases the pericycle serves as separating layer between the stele and the cortex. 

Types of stele:- 7 types of steles are found in the whole plant kingdom -

1. Protostele

2. Siphonostele

3. Solenostele

4. Dictyostele

5. Polycyclic stele

6. Eustele

7. Atactostele

Note:- Out of these the first 5 types of steles are found only in the stem of pteridophytes. Eusteel is found in the stem of gymnosperms and dicots. Atactostele is found in the stem of monocots.

Note:- The development of stele has also happened in this sequence. Atactosteel is considered to be the most advanced type of stele.

1. Protostele:- This is the most primitive type of stele in which the pith is completely absent and the phloem surrounds the xylem. According to Jeffrey (1898), the protostele is primitive type of stele in vascular plants.

On the basis of the shape of the xylem in the cross section, it is of 4 types -

i. Haplostele:- The xylem appears circular in cross section. It has been observed in fossil genera like Rhynia, Horneophyton and living genera like Selaginella chrysocaulos, S. kraussiana, S. selaginoides, S. willdenowi, Gleichenia dichotoma, Lygodium and Cheiropleuria. 

ii. Actinostele:- The xylem appears star shaped in cross section. Brebner (1902) named such a protostele as actinostele. Eg.- Asteroxylon, Psilotum, Lycopodium serratum and Sphenophyllum. 

iii. Plectostele:- In cross section, the xylem appears as parallel plates. Eg.- Lycopodium clavatum and L. volubile.

iv. Mixed protostele:- In cross section, the xylem is seen scattered in the form of segments. Eg.- Lycopodium cernuum

2. Siphonostele:- In this, pith or pith cavity is found in the center around which vascular tissues are found.

Origin of siphonostele:- There are different views among scientists regarding the origin of siphonostele. But they all agreed that the siphonostele originated from protostele by the formation of a pith in the center. Here, the centrally placed xylem core is replaced with a parenchymatous pith.

Different stages of changing protostele to siphonostele can be observed in the T.S. at different levels in Gleichenia, Osmunda, and Anemia.

There are two views regarding the origin of pith in the siphonostele.

i. Jeffrey’s theory:- 

- According to this theory, the pith is formed as a result of the invasion of cortical parenchymatous cells into the stele. The invasion of the pith occurs through the leaf gap or branch gap.

- Thus pith and cortex are homogeneous structures according to this theory.

- This theory is not accepted by most of the authors since in many pteridophytes there is a stele without leaf gaps but having siphonostele.

ii. Boodle’s theory:- According to the theory proposed by Boodle (1901), and Gwynne Vaughan, the siphonostele has evolved from the protostele by a transformation of the inner vascular tissue into the parenchyma.

On the basis of the location of phloem it is of two types –

i. Ectophloic siphonostele:- Phloem is found around the xylem. Eg.- Osmunda, Schizaea, etc.

ii. Amphiphloic siphonostele:- Phloem is found at both outside and inside the xylem.  Eg. Rhizome of Marsilea, Adiantum, Dipteris.

3. Solenostele:- The vascular tissue in the ectophloic siphonostele forms a leaf gap when it enters the leaf as a leaf trace.

4. Dictyostele:- When the leaves are found densely, many leaf gaps come together causing the vascular tissue of the amphipholic siphonostele to break into many pieces. Each piece is called a meristele and each meristele is a haplostele. In this way many merysteles are found in the form of a circle.

5. Polycyclic stele:- When 2 or more cycles of meristeles are found.

6. Eustele:- When vascular bundles are found in a circle.

7. Atactostele:- When vascular bundles remain scattered throughout the ground tissue.

Ans.

Study of sporophyte:-

> In most of the species of Ophioglossum and Botrychium the sporophyte has a short, erect, subterranean rhizome. In O. pendulum and, intermedium the rhizome is markedly dorsiventral.

> The lamina of the leaf in most species except in few species as e.g. O. palmatum is simple, entire and narrowly linear to broadly oval in outline.

> In O. palmatum the mature leaves are more or less clearly dichotomous and the lamina is palmately divided into a number of norrow lobes.

> In O. pendulum the long, pendent leaf may reach a length of 1.5 mm or more.

> The roots may be unbranched in sub genus Euophioglossum or branch freely in subgenus ophionderma or branch freely in subgenus churoglossa. 

> The roots are mycorrhizic.

Reproduction:-

> The sporangia are born on fertile spike that arise on the basal portion of the sterile leaf.

> After maturity the sporangium delisces by a transverse cleft in Ophioglossum.

> L.S. spike or cone:- All sporangia are at the same stage of development.

> Prothalus:- Spore germinates to give rise subterrenian prothallus.

> Embryo is always exoscopic.