6 FKRTILITY AND FERTILIZER HINTS 



light as long as the food supply in the seed lasts, but they will 

 be white and will not produce seed. By the aid of sunlight the 

 materials gathered by the root hairs and leaves are manufactured 

 into compounds and retained by the plants. 



The Food of the Plant. — The plant keeps growing until it pro- 

 duces seed. It may continue its growth for years as is the case 

 with trees. In this continual growing process we cannot see 

 the plant feeding but we know its nourishment is obtained from 

 the soil, water and air. The food of the plant, then, consists of 

 the mineral substances, water and gases taken from the soil and 

 air. 



Composition of Plants. — All plants are made up of water and 

 dry matter. The water is composed of hydrogen and oxygen 

 while the dry matter contains many elements and combinations 

 of elements. 



Water. — All plants and parts of plants contain water. The 

 water is present in two forms, namely, physiological and hygro- 

 scopic. 



1. Physiological water is that which is contained in the plant 

 structure. It is obtained from the soil. It is used to keep the 

 leaf tissues and their cell walls moist so that carbonic acid gas 

 may be absorbed, to transfer food materials, and to regulate the 

 temperature of the plant by means of evaporation of water, just 

 as the temperature of the animal body is regulated by the evapora- 

 tion of perspiration. When green grass is dried in the sun the 

 loss in weight is mostly due to evaporation of physiological water. 



2. Hygroscopic water is that which is taken up from the air 

 and may vary from day to day according to the humidity of the 

 surrounding air. On rainy days more water would be taken up 

 than on dry days. The writer has often determined the water 

 content of the same samples of corn meal, wheat bran, cotton- 

 seed meal, hays, etc., on different days and found variations 

 often of two per cent. Sometimes there is an increase and at 

 other times a decrease of hygroscopic water, depending upon the 

 humidity of the surrounding air. The hygroscopic moisture also 

 varies with different plant materials. 



