284 SCHREINER AND REED: EXCRETIONS BY ROOTS 
study of the antagonism existing between the roots of grass and 
those of fruit trees. They found that the grass roots had an actively _ 
malignant action upon the tree roots which could only be due to 
some action similar to that of direct poisoning. 
Jones and Morse (’03) reported a remarkable case of antago- 
nism between the butternut, /ug/ans cinerea, and cinquefoil, Poten- 
tilla fruticosa. The Potentilla was often killed under and around 
the butternut trees on a circle of fully twice the diameter of the 
tree top. Potentilla grew vigorously beneath other species of trees 
without any injury. They found that wherever the Fotentil/a was 
killed or dying its roots were intertwined and in close relation 
to those of the butternut trees. The death of the Porentilla seemed 
to be caused by some relation to, or effect from, the roots of the 
trees. 
Another illustration of the antagonistic action of one plant 
upon another has been given by Jensen (’07), who studied the 
effect of tree roots upon wheat under experimental conditions. He 
found that the action of the tree roots had a remarkably depress- 
ing effect upon the growth of wheat. The harmful effect was 
especially marked with certain trees like Pinus and Acer, while 
others like Prunus were less harmful. The growth of the wheat 
was most retarded during the summer season when the trees were 
physiologically active. When, in the autumn, the trees became 
ormant, the growth of wheat was much improved. 
An examination of the literature dealing with the growth of 
the lower plants shows that different workers have found that the 
growth of these plants often gives rise to unfavorable conditions in 
the surrounding medium. Some typical and instructive examples 
are described by Pfeffer in his Physiology of plants (1: 512; Eng- 
lish translation by Ewart). 
Bacteriology has demonstrated quite clearly that deleterious 
substances are formed during the growth of cultures. Eijkman 
(04) has studied the reaction of the waste products of a number 
of bacteria upon the same and other species. He found that the 
organisms produced without exception thermolabile substances 
which inhibited growth. The inhibiting substances were diffusi- 
ble but could not be filtered through a porcelain filter ; they were 
destroyed when heated toa temperature at which the organisms 
