PLANT GROWTH. 11 



soluble food the radicle and plumule are nourished ; they 

 rapidly increase in size, emerge through the coats of the 

 seed, and, if the external conditions are suitable, soon 

 commence their separate functions as root and leaf. The 

 process of germination may be easily studied in the 

 ordinary operation of malting barley. 



Seeds buried too deeply in the soil may not germinate 

 for lack of oxygen. Or if germination takes place the 

 plumule may fail to reach the surface, the store of food in 

 the seed being exhausted before the layer of soil is pene- 

 trated, and daylight reached. The smaller the seed, the 

 less, as a rule, 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 the root preponderate in the 

 young plant ; 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 being transferred from the root, leaf, and 



