216 MINUTE ANATOMY OF FLOWERING PLANTS 



vacuoles is the cell sap. It is sometimes colored. The 

 red and yellow colors of healthy leaves are generally due 

 to colored cell sap in some of the cells, masking the 

 green of the chlorophyll granules. Bright colors of fruits 

 and flowers also are generally due partly to colored cell 

 sap. The cell sap may contain sugar in storage, as it does 

 in the root of the sugar beet and in the stem of the sugar 

 cane. 



Certain substances belonging to the class oi formed mat- 

 ters (non-protoplasmic) are of such frequent occurrence 



and are produced in masses of such 

 size in the cell that they should be 

 briefly described. 



499. Starch. — Starch is the form 

 in which elaborated plant food is most 

 commonly stored. It is laid down in 

 the cells of storage organs, e.g. tubers, 

 in rounded granules (Fig. 363). When 

 these are considerably magnified they 

 are seen to be stratified, in evidence of 

 the mode of deposition of the starch in successive layers. 

 If the granules are 

 closely packed to- 

 gether, they may 

 become angular in- 

 stead of rounded. 



500. Protein^ gran- 

 ules and crystals. — 

 The external stor- 

 age cells of wheat 

 grains afford exam- 

 ples of protein gran- 

 ules (Fig. 364). The 



contents OI these 3(34. Transverse section near the outside of a Wheat 



cells make up the 

 so-called gluten of 



^ Protein is the name given to organic substance, whether of animal or 

 of vegetable origin, containing nitrogen and a small proportion of other 



363. Starch cells from 

 Potato tuber. 





grain : a, the husk (pericarp, integuments) ; 

 h, cells with protein granules; c, starch 



cells. — TSCHIRCH. 



