Secretory tissue of plants (special tissues)

• The tissues that are concerned with the secretion of gums, resins, volatile oils, nectars, latex and other substances are called secretory tissues.
• These are of great economic importance.
• These tissues are divided into two groups. They are:

A) Laticiferous tissue 

B) Glandular tissues

A) Laticiferous tissue

• These consist of thin walled, greatly elongated and much branched ducts containing a milky white juice known as latex.
• Laticiferous ducts, in which the latex is found may be of two types- latex cells or non-articulate latex ducts and latex vessels or articulate latex ducts.
• They contain numerous nuclei which lie embedded in the thin lining layer of protoplasm.
• They occur irregularly distributed in the mass of parenchymatous cells.
• The function of laticiferous duct is not clearly understood.
• They may act as food storage organs or as reservoirs of waste products.
• They may also act as translator tissues.

a) Latex cell or Non-articulate Latex Ducts

• These ducts are individual units which extend as branched structures for long distances in the plant body.
• They originate as minute structures, elongate quickly and by repeated branching ramify in all directions but do not fuse together.
• Thus network is not formed as in latex vessels.
• Such ducts are commonly found in Euphorbia, Nerium, Calotropis, etc.

 

    

b) Latex vessels or Articulate Latex Ducts

• These ducts or vessels are the result of anastomosing of many cells together.

• They grow more or less as parallel ducts which by means of branching and frequent anastomose form a complex network.
• Latex vessels are commonly found in many angiospermic families like Papaveraceae., Compositiae, Euphorbiaceae, Moraceae, etc.

B) Glandular tissues

• This tissue consists of special structures; the glands.
• These glands contain some secretory or excretory products.
• A gland may consist of isolated cells or small groups of cells with or without a central cavity.
• They are of various kinds and may be internal or external.

i) Internal glands

The common internal glandular tissues are as follows:

i) Oil glands secreting essential oils, as in the fruits and leaves of orange, lemon, etc.

ii) Mucilage secreting glands, as in the betel leaf.

iii) Glands secreting gum, resin, tannin, etc.

iv) Digestive glands secreting enzymes or digestive agents.

v) Special water-secreting glands at the tip of veins.

   

ii) External glands

These are commonly short hairs tipped by glands. They are:

i) Water- secreting hairs or glands

ii) Glandular hairs secreting gum-like substances as in tobacco, plumbago, etc.

iii) Glandular hairs secreting irritating, poisonous substances, as in nettles

iv) Honey glands, as in carnivorous plants.

References:

i) https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.1988.tb04159.x

ii) https://old.amu.ac.in/emp/studym/99991847.pdf

Secretory tissue of plants (special tissues)