Seeds and Seed Sowing 27 
moisture to the seed leaves. There a chemical change sets 
in. The dry, stored food is changed into liquid plant food. 
The temperature rises with this change, and our seeds 
become what is termed heated, and therefore perish. 
When seeds are sown, the skin allows only a limited 
supply of moisture to get through at a time. Thus the 
change — food substance to food — goes on slowly, as re- 
quired by the baby plant. The skin also helps to pro- 
tect this embryo in its earliest stages from attacks by 
disease germs in the soil. In the bean there is a con- 
siderable amount of food stored up, but in smaller seeds 
there is naturally a much less quantity. For example, 
the Shirley Poppy seed contains a very small amount of 
food substance. Now this ought to tell us about what 
depth to sow our seeds, because by the time all the food 
stored up is exhausted, the plant should be above the 
soil. Its roots will be penetrating into the ground and 
will be absorbing food substances from it. These sub- 
stances, however, are in a raw state, and must be manu- 
factured into the proper food for the plant, in the green 
leaves, under the action of sunlight. 
If the plants, therefore, have not reached the surface of 
the soil, and spread out their leaves to the sun before all 
the food is used up from the seed, the plant will die of 
starvation. Therefore, beans should be planted from 2 \ 
to 3 in. deep, and the smaller seeds at decreasing distances, 
until we come to the very smallest seeds, such as those of 
the Calceolaria, which should be sown on the surface, and 
lightly pressed into the soil. 
We will now turn our attention to the baby plant itself. 
It is a living thing, and all living things require air. 
