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 trichomes jointed and with the terminal cell bent in Pupalia, uniseriate tricbomes with a long terminal cell in Achyranthes, adpressed uniseriate 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 characteristic 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 .
