Velamen Tissue:-
· This is a special type of tissue found in the roots of orchid plants, which is dead and hygroscopic in nature.
· Orchids:-
Ø These plants are members of the monocot family Orchidaceae.
Ø These plants are found in temperate regions in mountain and cold areas.
Ø In the dense forests on the mountains, the sunlight does not reach the ground. Therefore, in order to receive sunlight, an ecological adaptation developed in it that it started living as an epiphyte on another tree 20-25 feet above the ground.
Ø Their roots are hanging in the air instead of reach 20-25 feet below, that is, aerial roots are found.
· In the roots of orchids, the velamen tissue is found between the epidermis and the exodermis.
· The cells of the velamen tissue are long and pointed which are called columnar cells. Due to the accumulation of Lignin and Suberin in these cells, the velamen tissue is of hygroscopic nature. This tissue absorbs water vapours directly from the atmosphere and makes it available to the plant.
· The velamen tissue is also found in the prop roots of Ficus benghalensis (Banyan tree), which absorbs water vapours from the atmosphere during the rainy and winter seasons. But the velamen tissue is found in relatively less amount in the prop roots of banyan.
Glandular Tissue:- The tissue which secretes various substances in the form of glands is called glandular tissue. These glands are of 2 types –
A. External Glands
B. Internal Glands
A. External Glands:- These glands are found on the outer surface of the plant organs. They are of 4 types –
1. Digestive Glands
2. Stinging Glands
3. Nectaries
4. Gummy Glands
1. Digestive Glands:- These glands secrete digestive enzymes.
Examples:-
i. Nepanthes (Pitcher Plant)
ii. Utricularia (Bladder wort)
iii. Drosera (Sun Dew)
iv. Dionea (Venus Fly Trap)
v. Aldrovanda (Water Fly Trap)
vi. Pinguicula (Butter wort)
Drosera:- It is a leaf like flat plant. On its surface there are hairs which secrete digestive enzymes in the form of droplets. These drops glow in sunlight. That is why it is called Sun Dew in common language.
2. Stinging Glands:- These glands are found in the form of hairs on the surface of the leaves and their secretion causes itching.
Example:- Urtica (Singing nettle)
Note:- When we go to the mountains to collect plants, then when our skin comes in contact with this Urtica, then it becomes very itchy. To stop this itching, there is another plant Spicea (wild spinach) near Urtica, which if rubbed on the skin, it ends itching. Thus Spicea acts as Antiurtica.
3. Nectaries:- Nectar is made in them. Generally these glands are found around the base of the sepals or the base of the stamens or around the ovary of the flower.
4. Gummy Glands:- These glands are found in the form of hairs and secrete a gum like sticky substance.
Example:- Tobacco, Plumbago, Boerhaevia
B. Internal Glands:- These glands are found inside the tissues of plant organs. These are of 4 types –
1. Lysigenous Tissue
2. Schizogenous Tissue
3. Hydathode
4. Laticiferous Tissue
1. Lysigenous Tissue:- When the cells of a tissue are destroyed and a cavity is formed in its place, then such tissue is called Lysigenous tissue and cavity is called Lysigenous cavity.
Example:- Maize
2. Schizogenous Tissue:- A cavity is formed when the cells of a tissue are not destroyed but start moving away from each other. Such tissue is called Schizogenous tissue and cavity is called Schizogenous cavity.
Example:-
i. Resin ducts:- Pinus, Helianthus
ii. Osmophores:- When Schizogenous tissue secretes essential oils it is called Osmophore.
Example:- Umbelliferae or Apiaceae
Volatile and aromatic oils are secreted by the members of this family, which are used for food and for making medicine.
Note:- In the fruits of fennel and cumin, lines are seen on the outside, whose numbers are 5 or 6. These lines are actually Schizogenous cavities.
Note:- Heeng (Ferula asafoetida) is mixed in digestive powder and also given to animals.
iii. These glands are also found in the members of Rutaceae family.
3. Hydathode:-
Ø It actually performs the function of excretion and is found only in some plants.
Ø These are found at the vein endings on the margin of the leaf.
Ø These are uncontrolled pores that are always open.
Ø Guttation:- It occurs through hydathode. So far, guttation has been observed in 365 plants.
Example:- Garden Nasturtium, Grasses
Ø In the winter of December, when there is no transpiration, this process of guttation occurs at night. Due to the root pressure, the water moves upwards and when it passes through the intercellular spaces of the epithem, the excretory substances mix in it and it becomes impure.
Ø Difference between Guttation and Transpiration:-
Ø In the month of December, at 4 - 5 am, the transpirated water can be clearly seen on the surface of the leaf in the form of dew and the guttated water can be clearly seen at the vein endings on the margin of the leaf.
4. Laticiferous Tissue:- The tissue that secretes latex is called Laticiferous Tissue. Latex is usually a milky substance. This tissue is of two types –
a. Latex cells
b. Latex Vessels
a. Latex cells:- These cells are elongated, multinucleated and branched. These cells are non-articulated i.e. they do not join together to form a network. Such ducts are called simple laticifers.
Examples:- Euphorbia, Calotropis, Nerium, Ficus religiosa, Vinca (Apocynaceae)
b. Latex Vessels:- These cells are articulated i.e. joint together to form a network. Such ducts are called compound laticifers.
Examples:-
i. Papaver somniferum
ii. Hevea brasiliensis (Euphorbiaceae)
iii. Ficus (Moraceae)
iv. Carica papaya
Note:- Milky latex is obtained from the unripen fruits of Papaver somniferum, which turns black when heated and exposed to air. Two main alkaloids are found in its latex which are used for medicinal purposes –
i. Morphene:- It is found in maximum amount in latex. It is used as LA (Local Anesthesia). Diacetyl Morphene (Heroine) is a synthetic narcotic.
ii. Codene:- This Alkaloid is added to Iodex, Moove etc.
Note:- Hevea braziliensis originated in Brazil. This plant is found abundantly in Karnataka state of India. This plant matures in 4-5 years and gives latex for more than 30 years. Rubber, bubblegum etc. are mainly made from the latex of this plant.
Note:- Argemone maxicana is a member of the Papaveraceae family, from which yellowish-white colored latex is obtained.
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