PLANTS OF THE INDIAN DESERT. 291 



changes in plants when they are raised in a place with a different 

 condition of soil and climate. Characters of hairs, therefore, will be 

 not only of very little value but will be misleading in the diagnosis of 

 orders, genera and species belonging to places differing greatly in 

 the condition of the soil and climate. 



In spite of all this, characters of hairs should not be altogether 

 neglected in the diagnosis of orders, genera, and species belonging to 

 the same place. For instance, shaggy hairs are found in Cleome, 

 peltate hairs in Gadaba candelabra hairs in Aeraa, uniseriate tricho- 

 mes jointed and with the terminal cell bent in Pupalia, uniseriate 

 tricbomes with a long terminal cell in Achyranthes, adpressed uni- 

 seriate hairs in Psoralea, hooked uniseriate trichomes in Alysicarpus 

 and two-armed hairs in Indigo/era. 



It is thus frequently found that certain types of hairs are char- 

 acteristic of the genera belonging to the same place, though not of the 

 species and orders. 



Glandular hairs are of not so common occurrence and are not 

 found in such abundance as clothing hairs. They are rarely found on 

 fleshy plants. The different types of external glands that occur on 

 desert plants are as follows : — 



(a) Club-shaped. — 



(1) With a stalk-cell and with a unicellular head, e.g., Bora- 



ginaceae and Labiatae. 



(2) With a stalk-cell and with a head divided by horizontal 



walls e.g., some Tlliaceac, some Go?ivolvulaceae and 

 some Gramineae. 



(3) With a stalk and a head divided by vertical walls, e.g., 



Verbenaceae. 



(4) With a stalk-cell and a head divided both by horizontal 



and vertical walls e.g., Sterculiace.ie, some Tiliaceae, 

 Papilionaceac, some Convolvulaceae and Acanthaceae. 



(b) Pitcher-shaped. — 



(1) With a stalk-cell and with a head divided by horizontal 



walls, e.g., Malvaceae. 



(c) (1) With a stalk cell and with a head irregularly divided, e.g., 



Malvaceae. 



(2) With a stalk cell and with a uniseriate or biseriate head 



e.g., some Gompositae. 

 {d) Capitate. — 



(l) W r ith a uniseriate stalk and with a unicellular head, e.g., 

 Geraniaceae, some Gompositae, Labiatae and Nyctag- 

 inaceae . 



