14 THE CHEMISTRY OF THE FARM. 



the seed being exhausted before the soil is penetrated and 

 daylight reached. The smaller the seed the less should 

 be the depth of earth with which it is covered. 



Plant Development. The development of the plant 

 after germination follows a regular course. With an 

 annual, which produces seed and dies during the first 

 season, we have first a great development of root and leaf, 

 which collect and prepare materials for growth; next 

 comes the formation of a flower stem ; and lastly, the pro- 

 duction of flower and seed ; after which the plant dies. 



The materials furnished by tho root preponderate in 

 the young plant, which is always extremely rich in nitro- 

 gen and ash constituents ; but as the plant matures the 

 proportion of carbon compounds derived from the action 

 of the leaves steadily increases. A cereal crop contains 

 at the time of full bloom all the nitrogen and potash which 

 is found in the mature crop ; the assimilation of phosphoric 

 acid continues somewhat later ; the increase of carbon and 

 silica proceeds as long as the plant is in a green state. 



When seed formation begins an exhaustion of the 

 other parts of the plant sets in; starch, albuminoids, 

 phosphoric acid, and potash, are transferred from the 

 root, leaf, and stem, and stored up in the seed. If the 

 season is a good one, and the development of the seed 

 fully accomplished, the straw of a cereal crop will be 

 found at harvest to be very thoroughly exhausted ; while 

 in seasons of limited production, or deficient maturity of 

 grain, the straw will retain far more of the materials 

 acquired during growth. For the same reason straw cut 

 while the crop is still green is far more nutritive than 

 when perfect ripeness has been attained. 



