PLAXT/XG THE SKED 25 



atively narrow foi- any one kind. The optimum temperature 

 for most of the small grains is around 80° Fahrenheit, though 

 germination begins at about 40°. Cotton and corn grow 

 best around 95°, and cotton will not germinate at all much 

 below 55°. Air is necessary for germination; for oxygen, 

 which is an important constituent of air, is needed for certain 

 chemical changes which tnke place in the plant food stored 

 in the seed. ^loisture is ' also needed, for these changes 

 take place only when water is present; it also furnishes a 

 medium bj^ which the food supph^^ is carried to all parts of 

 the. young plant. Plant food from outside sources is not 

 necessar}^ for germination, nor is light. These are required 

 for continued growth, but germination v/ill take place with- 

 out them. (See laboratory exercises at the end of this 

 chapter.) AVhen planted in the soil, the radicle naturally 

 goes down, while the plumule pushes up to the light, no 

 matter in which position the seed is planted. 



22. Planting the Seed. To apply these facts in a practi- 

 cal way, we can readily see that it is useless to plant most 

 seeds till the soil and the air are warm, though such plants 

 as oats and wheat grow best at fairly cool temperatures. 

 For this reason, they can be sown much earlier than cotton 

 or corn can be planted. The soil should be fine and mellow, 

 and the seed should not be covered too deeply, otherwise the 

 necessary supply of air will be shut off and the supply of 

 plant food in the seed will not be sufficient to enable the 

 young plant to reach the surface. A soil that is cloddy or 

 crusted is unfavorable for germination, as it is more diffi- 

 cult for the tender shoots to force their way through it. 



The depth of covering and the fineness of the soil desirable 

 for best results depend largely on the size of the seed and the 

 consequent store of plant food it contains. Seed must be 

 planted deep enough so that it does not dry out after germi- 

 nation starts, yet not so deep that the plantlet will have 

 difficulty in reaching the surface. Such coarse seeds as corn 



