THE CELL. 85 



in the form of starch grains. Here it is stored for subse- 

 quent use by the plant, and from this reservoir the plant 

 draws nourishment as needed. The tubers of the Potato, 

 Hyacinth bulbs, and seeds of various plants, are examples of 

 an accumulation of this reserve material. Besides starch, 

 aleuTone grains (or proteine grains) are formed in ripe 

 seeds and tubers. These are minute grains of albuminous 

 matter (Fig. 193), often containing roundish or clustered 

 granules, called globoids (Fig. 193, gl). Other inclusions 

 are sometimes present, called Crystalloids (Fig. 193, cr) ; 

 these are bounded by plane surfaces, and they, therefore, 

 resemble crystals, except in their behavior 

 with re-agents. They absorb water, and 

 change their angles. Their exact nature, 

 like that of aleurone, is not well under- 

 stood, though they appear to be modifica- 

 tions of protoplasm. 



109. The cell-sap (Fig. 172, v) is the 

 ■watery fluid contained in the vacuoles 

 of the protoplasm. It holds in solution the food materials 

 absorbed by the plant, as well as the surplus of the pro- 

 ducts of assimilation. One important constituent is sugar. 

 There are two varieties : the sucrose, or cane sugar, exist- 

 ing in abundance in Sugar-Cane, Sugar-Maple, Sugar Beet, 

 Indian Corn, and other plants ; and the glucose, or fruit 

 sugar, found in Grapes, Cherries, Gooseberries, and Figs. 

 The two kinds may exist together, as in Apricots, Peaches, 

 Strawberries. A substance related to starch and sugar, 

 and dissolved in the cell-sap, is inuline. It may be pre- 

 cipitated, when it takes the form of sphere-crystals (Fig. 



Fig. 193. Aleurone grains in the cells of the endosperm of the Castor Oil Bean; 

 gl, globoids ; cr, crystalloids. 



