108 PLANT LIFR ON THE FARM. 
has been the most prominent grass, while Lathyrus pra- 
tensis has manifested considerable increase, and Rumex 
Acetosa has been the most prominent among the miscel- 
laneous plants. 
The greatest change after some years was, however, 
not in the distribution of the species, but rather in the 
character of their development and their increased 
tendency to form stem and seed. 
Summary.—From the foregoing details it is manifest 
that the plants found on the several plots vary very 
greatly in number, in character, and in degree of de- 
velopment, according to the nature of the manurial 
agent employed, the ever varying character of the sea- 
sons, and the association or hostile competition of their 
neighbors. ‘These several conditions rarely, if indeed 
ever, act singly, but almost always in combination. Cir- 
cumstances are never exactly twice alike; a condition of 
absolute equilibrium is never attained. The nearest ap- 
proach to it has been reached in the case of the unma- 
nured plot on the one hand, and of the very highly ma- 
nured. plots on the other, but these, like the others, are 
influenced by climatal changes occurring now at one 
stage of growth, now at another. And even when a’ 
comparative staje of equilibrium is attained, very slight 
causes, even such as may be roughly called accidental, as 
the injuries inflicted by insects, or parasitic fungi, suffice 
to disturb the balance and bring about a different arrange- 
ment and proportion of species, and a corresponding 
change in the development of individual plants. 
As to the action of manures on the plants, it is com- 
paratively rarely that they are employed in such quanti- 
ties as to be absolutely destructive or poisonous. In most 
cases—even when a particular manure is proved to be 
more or less directly injurious to particular plants—the 
indirect harm accruing from the beneficial action of the 
