FOLIA SENN.E. SENNA. 1 79 



In the leaves of evergreens that are exposed to ex- 

 tremes of cold this same adjustment is apparent. 



The important parts of the leaf from the technical stand- 

 point are, however, the trichomes. These are appendages 

 or outgrowi;hs of the epidermis, and their shapes, sizes, 

 and characteristics are of great importance. Two main 

 types of Trichomes are to be distinguished : 



1. Glandular Hairs. 



2. Trichomes proper. 



Glandular hairs are, properly, hairs that contain 

 secretions. Trichomes proper exist in almost every 

 conceivable variation, from simple papillae to many 

 branched and shield-like hairs. 



Other important modifications of the epidermis are the 

 stomata. These are peculiarly modified cells, as a rule 

 oval to kidney-shaped, on a surface vein between which 

 a space is left for the passage of gases into the cavity 

 beneath.* 



FOLIA SENN^. SENNA. 



Senna is the leaves of Cassia acutifolia and Cassia 

 angusti folia; plants of eastern and central Africa and 

 India. Cassia acutifolia is the Alexandrian senna, 

 Cassia angtistifolia, the Indian, especially fine qualities 

 of which have received the name of Tinnevelly. This is 

 said to come from Arabian seeds cultivated in southern 

 India. 



Description. — The leaves of Cassia acutifolia are 3 

 to 5 cm. long and 9 mm. broad, lanceolate or lance- 

 oval, subcoriaceous, brittle, rather pointed, equally 

 oblique at the base, entire, grayish-green, somewhat 

 pubescent, of a peculiar odor and a nauseous, bitter taste. 

 Cassia angustifolia leaflets are from 3 to 5 cm. long 

 and 10 to 15 mm. broad, lanceolate, acute, unequally 



♦ For a more detailed study of the Leaf, consult *' Morphology and 

 Histology of Plants," Rusby and Jelliflfe. 



