Germination of Forest Trees 17 



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 



