SENNA 33 



Microscopical Characters. The epidermal cells of both surfaces have straight 

 walls and many contain mucilage ; the stomata are surrounded by two cells 

 with their long axes parallel to the ostiole ; the hairs are one-celled, thick- 

 walled, warty, and often curved. Both surfaces possess long, narrow palisade 

 cells. The midrib contains abundant pericyclic fibres, abutting on which are 

 cells containing prismatic crystals of calcium oxalate, cluster crystals of which 

 occur in the mesophyll. 



The student should observe 



(a) The predominating asymmetrical, lanceolate or ovate-lanceolate 



shape, 



(b) The veins distinct on the under surface, 



(c) Both surfaces more or less distinctly pubescent ; 



and should compare the leaves with 



(i) Mecca senna leaves, which are elongated lanceolate, 

 (ii) Indian senna leaves, which are yellowish green in colour, 

 less conspicuously asymmetrical, and less pubescent. 



Mitt 



FIG. 21. Obovate Senna leaves (C. obovata). Natural size. 



Constituents. According to the very exhaustive researches of 

 Tutin the chief constituents of Alexandrian senna are rhein, aloe- 

 emodin, kaempferol and isorhamnetin, all four substances occurring 

 both free and in the form of glucosides ; myricyl alcohol and a phyto- 

 sterolin (phytosterol glucoside) are also present. The leaves contain 

 in addition mucilage, calcium oxalate, resin, and amorphous glucosidic 

 material. 



Aloe-emodin, C 14 H 5 O 2 (OH)2CH 2 OH, brownish green needles, is 

 hydroxymethyldihydroxyanthraquinone and is the primary alcohol 

 corresponding to chrysophanic acid (better termed chrysophanol) 

 which is dmydroxymethylanthraquinone. Rhein, C 14 H 5 2 (OH) 2 COOH, 

 orange needles, is the corresponding carboxylic acid and may be 

 formed by the oxidation of aloe-emodin. Both aloe-emodin and rhein 

 exist in the free state and in the form of glucosides. 



Ksempferol, C 15 H 6 2 (OH) 4 , is 1:3: 4-trihydroxyflavonol (bright 

 yellow needles), and is yielded together with dextrose by the hydrolysis 

 of ksempferine, C 27 H 30 16 ,6H 2 0, which is also present in senna. 



Isorhamnetin, C 6 H 12 O 7 , yellow needles, was first obtained from 

 yellow wallflowers. 



Of these constituents aloe-emodin and its glucoside appear to be 



3 



