1 82 PLANT ORGANS OR PARTS OF PLANTS. 



The parenchymatic tissue is the characteristic mes- 

 ophyll of leaves ; in fresh powders the chlorophyll grains 

 are prominent and numerous. The stomata are held to 

 be characteristic by some writers, but exhibit great 

 variety in form. 



The elements of the leaf stalks and veins are usually 

 conspicuous, lying in small masses ; the vessels, spiral or 

 annular, are of the usual form; from the midrib or leaf 

 stalk pitted vessels may be found, also a certain propor- 

 tion of fibres; some short bast fibres may be found 

 in the mesophyll. 



Chemistry. — The active principle is probably cathartic 

 acid, a black amorphous glycoside. Besides this, there 

 are sennapicrin, a bitter substance, crystallizable sugar, 

 cathartomannite, and also chrysophanic, malic, tartaric, 

 and oxalic acids, with mucin, tannin, and traces of a 

 volatile oil. The ash constitutes i to 12 per cent. 



FOLIA DIGITALIS. DIGITALIS. 



" The leaves of Digitalis purpurea, Linne (nat. ord. 

 ScrophularinecB) , collected from plants of the second 

 year's growth." 



Digitalis is a handsome biennial herb, 2 to 5 feet high, 

 growing in sandy or gravelly soil in the mountainous 

 forests of Western Europe, from Norway to southern 

 Spain. It is cultivated as a garden plant, and, to some 

 extent, for the drug market. 



Leaves of the second year's growth only should be 

 collected. They should be full-grown, gathered at the 

 time of flowering, or, according to F. Schneider, during 

 the late summer or early fall. The preservation of the 

 virtues of the drug requires great care in drying. The 

 leaves become inactive in about one year. The seeds, 

 though little used in the United States, are stronger and 

 more permanent. 



Description. — The lower leaves are narrowly oval in 



