300 <A TEXTBOOK OF GENERAL BOTANY 
The source of energy in germination is respiration, or, in 
other words, the oxidation of food material stored in the seed. 
The amount of energy necessary is considerable, as germina- 
tion requires that the material stored in the seed be rapidly - 
transformed into tissues. Large quantities of oxygen are there- 
fore necessary, and seeds will not germinate unless there is an 
yd EULE 
TE } Sy 
\ 
BEN | 

Fig. 305. Successive stages in the germination of castor-oil seed 
The cotyledons first act as absorbing organs and later become green foliage 
leaves. Compare with Fig. 269 
abundant supply. For this reason most seeds fail to germinate 
in poorly aérated soil, as when buried at a great depth or when 
the air spaces of the soil are filled with water. 
Selection of seeds. The value of knowing the hereditary 
characters that are carried in a seed has already been discussed. 
In selecting the seeds for planting there are certain other points 
which it is important to take into consideration. Among these 
are the size and vigor of the plant producing the seed, and the 
size of the seed itself. Vigorous plants are more likely to pro- 
duce vigorous offspring than are weak ones. Moreover, large 
seeds are much more likely than small ones to give rise to robust 
plants. A large seed indicates vigor and abundant food material 
for the nourishment of the young plant. Care should be taken 
