526 



A TEXT-BOOK OF BOTANY. 



The leaves contain oxalic acid, both free and in combination with 

 calcium and potassium (Fig. 290). 



Fig, 292. Bnckwheat {Fagopyrum esculentum): A, transverse section of grain showing 

 pericarp (c), endosperm (n) and slender coiled embryo (e) ; B, transverse section of portion 

 of grain showing epicarp (e), fibrous layer (f), pigment layer (p), outer epidermis of spermo- 

 derm (o), aleurone cells (a), endosperm cells containing starch (n); C, surface view of cells 

 of epicarp; D, isolated fibers of pericarp; E. surface view of aleurone cells; F, isolated par- 

 enchyma cells of endosperm filled with starch grains as seen in buckwheat flour; G, appear- 

 ance of starch grains when mounted in oil and viewed with polarized light ;_ H, swollen and 

 altered starch grains which are two to three times the size of the normal grains. 



Tannin is obtained from a number of the plants belonging to 

 the Polygonaceae, as the root of Rumex hynienosepalus of Texas 



