SEEDS AND SEEDLINGS 



159 



cot 



150. Kinds of plant food found in seeds. All seeds contain 

 some protein material, though frequently it is present only in 

 small quantities. Carbohydrates 

 (in the form of starch, sugar, and 

 cellulose) and fats or oils also 

 occur. Many other substances, 

 such, for example, as the poison- 

 ous compounds that occur in the 

 seeds of larkspur and Jimson 

 weed, and in the castor 

 bean, the opium poppy, 

 and nux vomica (out 

 of which strychnia is 

 made), are character- 

 istic of certain seeds. 



The reserve protein 

 is indispensable, since 

 it is the basis of proto- 

 plasm, without which 

 life cannot exist nor 

 growth take place. 

 Other reserve foods 

 serve mainly to sup- 

 ply building material 

 for the plant body 

 until it can draw raw 

 materials freely from 

 the soil and the air 

 and carry on photo- 

 synthesis for itself. 

 For this purpose the 

 rice grain supplies 

 mainly starch ; the 

 Brazil nut, oil; the 

 grain of Indian corn, both starch and oil ; and date seeds or 

 coffee seeds, cellulose. Of the substances mentioned proteins, 



FIG. 142. Two stages in the growth of the 

 bean seedling 



In the younger stage the arch of the hypocotyl is 

 but little above the surface ; in the older stage the 

 cotyledons have separated, the first internode has 

 elongated considerably, and the first pair of foli- 

 age leaves has expanded, cot, cotyledon; h, hy- 

 pocotyl ; ha, hypocotyl arch ; i, internode ; I, leaf ; 

 r 1; taproot, which proceeded from the tip of the 

 hypocotyl; r 2 , branches of r. Natural size 



