64 



BOTANY 



Imbedded in the protoplasm there may be detected various solid, 

 or semi-solid, substances which are secondary products of the proto- 

 plasm. The commonest of these are granular, and are either of 

 albuminous nature, like the gluten-granules in the outer cells of the 

 wheat-grain, or carbohydrates, of which starch is the commonest 

 form. These are especially abundant in the cells of seeds, spores, 

 tubers, and other stores of reserve-food. 



Starch. Starch is one of the commonest products of the cell, and 

 often occurs in great quantities in the cells of structures like bulbs, 

 tubers, seeds, and similar reservoirs of reserve-food. Thus potatoes, 

 grains of various kinds, Arrowroot, Sago, etc., owe their value as 



al 



FIG. 35. A, a cell from the endosperm of Ricinus communis, showing aleurone- 

 grains, al, containing albumen-crystals and globoids (x 500). B, cell from the 

 dry cotyledon of Pisum sativum, filled with small aleurone-granules, al, and 

 large starch-granules, st (X 500). C, two large starch-granules from the rhizome 

 of Canna Indica (X 250). 



food largely to the starch contained in their cells. Starch appears 

 in most chloroplasts as the first visible product of the assimilation 

 of C0 2 , and this starch may be used at once for the growth of the 

 tissues, or it may undergo a change into a soluble compound (usually 

 glucose), which is conveyed to the cells where the reserve-starch is 

 reconstructed from the glucose, this process being independent of 

 light, which is essential for the original manufacture of the starch. 

 As in the green cells, the formation of reserve-starch is also bound 

 up with the plastids, here known as starch-formers. 



Starch-grains (Fig. 35, B, C) are usually ellipsoid, or the smaller 

 ones globular, this difference being due to the fact that the smaller 



