SEEDS AND SEEDLINGS 159 
150. Kinds of plant food found in seeds. All seeds contain 
some protein material, 
though frequently it is present only in 
small quantities. Carbohydrates 
Cn 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, 
coffee seeds, cellulose. 
ha 
Fie. 142. Two stages in the growth of the 
bean seedling 
In the younger stage the arch of the hypocotyl is 
put 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; 7, internode; J, leaf; 
r 1, taproot, which proceeded from the tip of the 
hypocotyl; rs, branches of ry. Natural size 
both starch and oil; and date seeds or 
Of the substances mentioned proteins, 
