223 



CHAPTER X. 

 THE PLANT. 



Foit a description of the structure and general life-history 

 of plants the reader will naturally turn, not to a work on agri- 

 cultural chemistry, but to a treatise on botany. 



Nevertheless, a brief account of the functions of the various 

 parts and their special adaptation for carrying on the processes 

 of life may usefully be given here. 



Germination. A seed is essentially a germ or embryo, 

 together with a store of reserve material from which the future 

 plant is to be formed (endosperm or cotyledons). The embryo 

 is the only portion of the seed which is really alive, the endo- 

 sperm, e.g., of barley or wheat, is merely a store of food; 

 hence it is possible to transplant the embryo from one seed to 

 another without destroying its power of growth. The nature 

 of the food stored in a seed varies ; there is always a con- 

 siderable amount of albuminoid matter and either starch or 

 fat. 



Seeds suffer little change by keeping, provided they be pro- 

 tected from moisture ; if not already dry they lose water, and 

 in some cases carbon dioxide, but these changes soon cease 

 and no further loss occurs. Vitality may be retained for 

 several years. When placed under suitable conditions seeds 

 germinate. The most important circumstances affecting ger- 

 mination are 



(1) Moisture. 



(2) Temperature. 



(3) Access of oxygen. 



(4) Removal of carbon dioxide. 



Moisture is essential and acts by producing considerable 

 swelling, accompanied by a rise of temperature. 



A suitable temperature is also requisite. As a rule no 

 germination occurs below 3 or above 49. The limits as 



