166 Gardening 
in the seed. A continual supply of water is therefore 
necessary. 
With the very beginning of growth, the embryo needs 
Aa Surface of soil 
Fic. 91. The germination of corn, bean, and squash. In the corn (a) the 
little plant pushes out both stem and root and grows upward, leaving the seed 
in the ground. In the bean (5) the root grows out and turns downward, and 
then the part just above the root grows into an arch and pushes upward, dragging 
the seed with it. After this the seed coat is burst open and the first two seed- 
ling leaves (cotyledons) are freed. In the squash (c) the seed coat is caught 
against a small ‘peg’ just above the root and held, while growth forces the 
cotyledons upward and pulls them out of the old coat. 
an additional and constant supply of oxygen for respira- 
tion. This comes from the air that is held in the spaces 
in the soil. But if water completely fills the spaces be- 
tween the particles of soil in which seeds are planted, the 
seeds will decay because of lack of air, just as they do if 
left in a dish with water covering them. Hence seeds 
germinate best when the soil about them is moist with 
capillary water but has no free water in it. 
A certain amount of warmth is necessary to start 
growth in a seed. The amount required is greater for 
seeds of warm-season vegetables than for those of 
cool-season plants. . In fact, the best temperatures for 
