AMERICAN INSTITUTE. 



263 



cally, on vrhicli germination mainly depends. Close examination has 

 incontestibly proved that germination essentially consists of numerous 

 chemical changes, which, for their development, require the presence of a 

 certain amount of heat, moisture, and air ; and to comprehend these pro- 

 cesses, it is necessary we should understand the conditions under which 

 they act. After discovering these, we will comprehend precisely what is 

 necessary to make a seed grow successfully. These, we have seen, are 

 moisture, air, and heat ; consequently, whenever a seed is so placed, ger- 

 mination must take place. 



Soil does not act chemically in the process of germination, but is merely 

 the vehicle through which a constant supply of moisture, heat and air may 

 be kept up. 



Keeping this statement in view, we can readily understand the conditions 

 of soil necessary to influence the future prospect of the crops. We must, 

 therefore examine into the mechanical relations of soil. This can best be 

 done by the aid of figures. 



Soil, mechanically speaking, consists of particles, which assume all sizes 

 and forms, from rocks to stones, pebbles, and finally, powder ; in all which 

 stages they are of such irregular shape that they cannot possibly lie so 

 close together as to prevent passages between them, owing to which fact 

 soil, in the mass, is always porous. I have frequently placed the smallest 

 particle of which soil is composed, under the magnifier, and have invariably 

 found it porous, and generally composed of broken vegetable tissue. Even 

 the finest dust from the road-side, present. d every imaginable variety of 

 structure and shape. 



Fig. 1. 



i'lg. 2. 





Fig. 3. Fig. 4. 



You will observe delineated on the black-board, four figures, giving a 

 rude representation of what the glass exhibited to me in my examinations 

 of soil, by which I may be enabled partially to illustrate the properties of 

 soil, mechanically speaking. 



By examining figure 1, you will observe that there are two classes of 



