294 THE JOURNAL OF INDIAN BOTANY. 



by a dense covering of hairs and by secretions from the internal 

 glands which thicken the watery contents in the plant tissue, so as 

 to be less easily transpired. 



Secretions. — The most common form of secretions is tannin 

 which shows itself by its yellowish colour and which occurs both in 

 the leaf and axis, or only in the leaf or axis. Another secretion of 

 usual occurrence is oxalate of lime in various forms of crystals and 

 occurring abundantly both in the leaf and axis. Silica is abundantly 

 deposited in outer epidermal walls of species of Cyperaceae and Gra- 

 mineae. Deposits of carbonate of lime are found in the walls of 

 clothing hairs of some species of Boraginaceae and in cystolith-like 

 structures in the basal epidermal cells of clothing hairs of some species 

 of Gucurbitaceae, Boraginaceae and in the enlarged epidermal cells 

 of the leaf of some species of Acanthaceae. Mucilaginous secretory 

 organs occur in a few orders as will be mentioned below. The epi- 

 dermal cells of the leaves of Zizyphus contain cellulose slime. Balsam 

 canals occur in the phloem of vascular bundles in Burseraceae. Con- 

 tents of some of the other secretory organs in the leaf and axis cannot 

 be determined with certainty as I had to deal with herbarium 

 material. 



The different types of secretory organs that occur in the desert 

 plants are as follows : — 



(a) Oxalate of lime. — 



(1) Clustered crystals e.g., Violaceae, Polygalaceae, Portula- 



ceae, Elatin'xe, Malvaceae, Tiliaceae, Zygophyllaceae, 

 Rhainneae, Sapindaceae, Moringaceae, Rosaceae, Lyth- 

 raceae, Onagraceae. Ficoideae, Asclepiadaceae, Borag- 

 inaceae, Convolvulaceae, Amarantaceae, Chenopodia- 

 ceae and Polygonaceae. 



(2) Solitary crystals, e.g., Sierculiaceae, Tiliaceae, Simarub- 



aceae, Burseraceae, Boraginaceae, Convolmdaceae and 

 Euphorbiaceae. 



(3) Acicular raphides e.g., Flcoideae, Rubiaceae, Compositae, 



Nyctaginaceae and Commelinaceae. 



(4) Styloids e.g., Ficoideae. 



(5) Clusters of acicular crystals, e.g., Menispermaceae and 



Gentianaceae. 



(6) Crystal sand, e.g., Rubiaceae, Solanaceae, Acanthaceae 



and Nyctaginaceae- 



(b) Calcium carbonate deposits, e»g., walls of hairs of Cruet' 



ferae and Boraginaceae. 



