10 



THE STORAGE OF FOOD IN THE SEED 



FIG. 7. Canna starch 



Magnified 300 diameters 



shape. The shape and markings of a starch grain, whether 

 found in the seed or in some other part of the plant, are often 

 sufficiently definite to serve to identify the kind of plant from 



which they came. Frequently the 

 markings are very regular and beauti- 

 ful, as in canna starch (Fig. 7). They 

 are due to the successive layers de- 

 posited as the starch grain is formed. 

 During the growth of the seedling, 

 seeds containing starch rapidly lose 

 it, and microscopical examination of 

 a sprouting grain of corn or of the 

 cotyledons of a bean plant several 

 weeks old shows the cells compar- 

 atively emptied of starch and those 

 grains which remain much eaten away, as described below. 



10. Action of ferments. A substance which can produce or 

 excite any one of the chemical changes known as fermentation 

 is called a ferment. The most familiar kinds of fermentation 

 are the alcoholic, by which alcohol is. produced, and the acid, by 

 which solutions of alcohol (such as fermented cider) are turned 

 into vinegar, and by which the sugar of milk is changed into 

 lactic acid when sweet milk turns sour. 



All these fermentations and many others are caused by the 

 development within the fermenting substances of minute living 

 organisms, either yeasts or bacteria, described in Chapter xxn, 

 which are consequently known as organized ferments. 



There is a class of substances which, without the presence of 

 yeasts or bacteria, can produce active fermentation. From the 

 absence of the organisms above-mentioned, these are called 

 unorganized ferments, and they are also known as enzymes. 

 One of these, diastase, plays a most important part in seeds 

 during germination, transforming starch into sugar. Diastase is 

 found in considerable quantities in malt, which is barley sprouted 

 and then quickly killed by moderate heating. Naturally, as a 



