GERMINATION OF SEEDS 19 



will be seen that the stems alone are making rapid growth. 

 They are becoming etiolated. The internodes will be long 

 but perhaps there will be no more of them. The stem will be 

 smaller in thickness and will be softer in texture. The leaves 

 will be small, with long petioles. If the roots are examined, 

 those of the plants grown in the dark will be found to be 

 smaller and poorly branched in contrast with those of the 

 plants grown in the light. This difference in the character 

 of growth is believed to be due to the effect of light on a 

 growth-regulating hormone. The plants grown in the dark 

 are heavier due to more water in the larger cells, but if the 

 dry weights of the plants are determined, it will be found that 

 the larger plant, grown in the dark, has not produced as much 

 plant material as the plant which was grown in the light. 

 The photograph (Plate XV) showing pea and radish seed- 

 lings, and the table on page 181 illustrate what happens 

 under these conditions. 



Some mineral salts are absorbed by the very young seed- 

 ling, but the amount is negligible in comparison with the 

 weight of the stored food or later with the weight of the 

 manufactured foods. A favorable supply of mineral salts in 

 the soil, however, will stimulate growth very early in the 

 seedling development. If a quickly available nitrogen fer- 

 tilizer is applied, it may increase the early growth of the 

 shoot, and cause the plant to be a little earlier in its flower- 

 ing and fruiting. 



Most seeds should be planted as shallow as possible in 

 order that they may get an abundance of oxygen, but deep 

 enough to give them constant moisture. While it is easier to 

 plant them too deep than too shallow, a good rule is to try to 

 cover them with a depth of soil four to six times the diameter 

 of the seed. A few seeds, such as some lawn grass seed, need 

 a little light to germinate best, and must, therefore, be cov- 

 ered very little if at all. If the soil around young seedlings 

 becomes so dry that water cannot enter the seedling, it will 



