Page:The Journal of Indian Botany.djvu/283

 Tephrosia, Aly sicar pus an d Rhyncosia. The veins are few and do not anastomose freely, which suggests that the leaves do not transpire vigorously.

The hairy covering consists of clothing and glandular hairs. Clothing hairs are of the nature of uniseriate trichomes and have varied forms as follows : —

(a) With walb smooth or muriculate as in H. latcbrosa, C. Burhia fig. 100 and species of Tephrosia, Phaseolus and Rhyncosia.

(b) Terminal cell bent in the form of a hook in A. vaginalis fig. 110.

(c) Terminal cell bent and lying parallel to the surface and with a muriculate surface in P. odorata fig. 108.

{d) Two-armed and formed of a stalk cell and of an unicellular two-armed terminal cell, the arms being equal in species of Indigo/era fig. 105.

The covering of clothing hairs in isobilateral leaves is not dense and it should be noted that two-armed hairs in Indigo/era, though few in number, are short-stalked and form a suitable light screen close to the surface of the leaf, against strong light and glare, which accelerates transpiration and is injurious to chlorophyll.

External glands are not found on the leaf of species of Heylandia, Crotalaria, Indigofera and Tephrosia. In species of Rhyncosia glandular hairs are formed of a short uniseriate stalk and of a spherical head fig. 114 ; they occur on both the surfaces. External glands in P. odorata and P. trilobus are club-shaped and consist of a short uniseriate stalk and of a head divided by horizontal and vertical walls. Glandular hairs in A. vaginalis are composed of a stalk-cell and a globose head, divided by horizontal and vertical walls ; they occur only on the lower surface of the leaf.

It should be observed that external glands are found in a small number of species and sometimes only on the lower surface.

Structure of the Axis: — The epidermis is two-layered in species of Heylandia, Crotalaria and Psoralea; it is single layered in species of Indigofera, Tephrosia, Phaszolus, Alysicarpus and Rhyncosia. The outer walls are thickened and are arched convexly outwards.

Hairy covering has the same character as of that on the leaf. It should be noted that glandular hairs formed of a multicellular stalk and of an irregularly divided head are found in I. argentea.

Internal secretory organs are represented by tannin sacs. They are abundant in species of Indigofera and occur in the cortex and pith. Some of the vessels in I. liniflolia also hold tanniniferous contents. Tannin sacs occur in the soft bast of species of Psoralea and Rhyncosia.