Germination of Forest Trees 7; 
which oxidizes the fats and oils of the endosperm. It has been 
noted that the quantity of oxygen absorbed is much greater in the 
case of fatty seeds, like those of the pines and birches, than in 
the case of the starchy ones, 
It has been known for a long time that seeds lose weight during 
the process of germination although no solid matter is lost as near 
as can be determined. If we take a certain quantity of seeds 
and weigh them both before and after germination, being sure 
to get the dry weight both times, we find that although the seeds 
have increased in size, they have lost weight. This is due to the 
loss of certain elements like carbon and hydrogen. In the process 
of respiration the carbohydrates in the endosperm are broken 
down, carbon and hydrogen are lost while the quantity of nitrogen 
remains practically constant. In the process of respiration, the 
products of combustion are carbon dioxide and water. 
Respiration in the seed is quite different from that in the case 
of leaves and other green parts of the plant. Seeds are generally 
not provided with intercellular air spaces, but oxygen penetrates 
to their interior chiefly by diffusion from cell to cell. Thus it will 
be seen that the supply of oxygen to the deep-seated cells of the 
seed is most liable to become insufficient. This of course retards 
germination. If the supply of oxygen is reduced materially, due 
to lack of soil aeration, germination may be prevented. The best 
aerated soils are those that have comparatively large interstitial 
spaces, like sands and gravels, and the poorest ventilated soils are 
the heavy loams and clays which are small grained and compact 
and have minute interstitial spaces. The seeds of different tree 
species naturally vary as to their soil requirements in this respect. 
This explains why tree species of sandy habitats germinate so 
poorly on clay soils. 
From what has been said, it will be seen that water, heat, and 
oxygen are the essentials for germination, and that the lack of any 
of these factors is sufficient to retard, if not entirely to inhibit the 
process, 
It is a well-known fact that seeds have a power of remaining 
dormant for a period without affecting their vitality. The power 
_to retain this vitality is due largely to the nature of the seed-coat 
