MICHIGAN ACADEMY OF SCIENCE. 
35 
wholly theoretical, is the assumption that undecomposed excretion (in small 
quantity) is stimulative to the growth of a radicle of another species. And 
there is experimental proof that toxic substances like copper sulphate when 
in very minute quantities, stimulate plant growth. 
As has been pointed out, the mutually injurious effects of plant roots 
would likely be very variable according to the species used, some distinctly 
harmful, and perhaps some neutral or even beneficial; though with the plant 
here examined none seemed materially beneficial. But it must not be 
forgotten that the plants used were seedlings which had a supply of organic 
food ready prepared, and were dependent only upon a supply of water and 
air. These conditions are not sufficient of course for plants which require 
other matter than water from the soil. When the question of complex 
nutrient solutions, or soil solutions, are taken into consideration, the ques- 
tion becomes so complicated that, beyond a few steps, it is at present not 
safe to go, for there is one thing very apparent that as soon as even one 
substance is introduced into the distilled water used as a root medium, the 
question becomes very complicated. At all events, there is one prominent 
deduction to be made from the distilled water culture. To get good growth, 
plants must be protected against their excretion, and against that of other 
plants. This protection is accomplished by oxidation, decomposition, and 
reduction of excrementitious organic compounds. From this it seems to 
me the question of crop growing is not so much one of fertilizers, as generally 
understood, as it is one of the purification of the soil from root excretion, 
and of a knowledge of what plants are mutually least injurious to one another. 
It is also clear that an important function of barnyard manure is to supply 
an abundance of bacteria which rapidly decompose the excretion, and reduce 
it to simple, non-injurious substances. 
A resume of the conclusions results in the following: 
During the first 24 to 48 hours, two seedling plants when grown together, 
often promote the growth of each other, but afterward, bacteria and aquatic 
fungi prey upon the dead cells of the root cap, and upon the dying root hairs, 
producing an excrementitious substance decidedly injurious to the roots. 
It is mainly the excretion of these fungi and bacteria which directly causes 
the injurious effects. 
When a plant is watered with plant juice, the first set of bacteria or fungi 
which attacks the juice results in a harmful matter; and it is not until the 
harmful matter is decomposed by other bacteria or by chemical action set 
up by manure, that the injurious causes are removed. 
The excretion of fungi is usually injurious to plant roots, excepting in 
the case of a symbiosis of mycorhiza and host; but from certain preliminary 
experiments it appears as though the excretion of such mycorhiza is in- 
jurious only to plant roots other than those of the host. 
And finally: 
The loose cells set free by roots are the prime cause of injury*, though not 
the direct cause. They furnish food for fungi and bacteria, but it is the 
excretion of these fungi and bacteria which causes the injury. 
Mycorhiza shows a step further in adaptation, inasmuch as they attach 
themselves to the roots, the first step being the attack on root-cap cells and 
root hairs set free. 
Remedies : 
♦For the root-cap cells alone the loose cells as estimated amount to nearly one-half as much as the 
total root. 
