STARCH 



9 



than can mature plants under the conditions of competition 

 with one another which they must encounter, and so plants 

 which shoot up rapidly at first possess a decided advantage. 

 There is also a much better chance for seedlings growing in 

 woodlands if they can attain considerable size before they are 

 too much shaded by the foliage of the trees above them. This, 

 of course, does not 

 apply to evergreen 

 woods. 



8. Kinds of food 

 stored in seeds. 

 The three princi- 

 pal kinds of plant 

 food, or reserve 

 material stored in 

 seeds, are starch, 

 oil, and albumi- 

 nous substances, 

 QY proteids^ A sin- 

 gle seed may con- 



FIG. 6. Section through exterior part of a 

 grain of ^^ 7 heat 



c, cuticle, or outer layer of bran; ep, epidermis; m, 

 middle layer; /, /i, layers of hull next to seed coats; 

 s, i, seed coats; p, layer containing proteid grains; 

 st, cells of the endosperm filled with starch. Greatly 



magnified. After Tschirch 



tain all three of 

 these in consider- 

 able proportions, 

 or it may contain 

 proteids together 

 with either starch or oil. Some proteids are always present, 

 since the power of the seed to live and grow depends upon 

 these compounds. 



9. Starch. Every one is familiar with the appearance of starch 

 in its commercial form. As found in seeds it occurs in micro- 

 scopic compartments known as cells (Fig. 6). Each cell contains 

 many small starch grains, usually of a nearly round or an ovoid 



1 As in general throughout the book, the statements of the text pre- 

 suppose a suitable amount of laboratory work ; for example, that of the 

 manual of the authors. 



