GENERAL, PRINCIPLES. 39 



herent vigor and in ability to grow quickly, as the soils 

 are wet and heavy of texture, and as the winter weather 

 is severe ajid the summer weather dry. 



The Grazing of Pastures. Much of what has heen 

 said in the preceding section on the grazing of meadows 

 will also apply to the grazing of pastures. But the pro- 

 ductiveness of the latter is likely to he injured more hy 

 excessive grazing than that of the former. Grazing is 

 excessive when it lessens the possible production of the 

 pasture, but it may not be easy to determine in many 

 instances when that point is reached beyond which fur- 

 ther grazing would be excessive, since ivhat would be 

 in excess in a season characterized by drought would 

 not be so in one characterized by an abundant rain- 

 fall. 



Close grazing injures pastures by weakening their 

 capacity to grow, by increasing their exposure to injury 

 through surface evaporation, by removing what would 

 prove a protection to them in winter, and in some in- 

 stances by preventing the plants from re-seeding. 



That plants breathe through the medium of the leaves 

 is well known. It follows, therefore, that the strength 

 of the plant, when amply supplied with food and mois- 

 ture will be proportionate to the extent of the surface 

 through which it breathes. This explains in part at 

 least why a larger amount of food will be furnished by 

 grass plants from a given area under normal condi- 

 tions when mowed than when grazed. But this result 

 will probably be modified when moisture is insufficient. 

 Consequently, the closer the grazing the less ordinarily 

 will be the production of the pastures. 



