Oe pee ee ee le oe ade ee ey ge ee ae OTs) 
SCHREINER AND REED: EXCRETIONS BY ROOTS 285 
were killed. The waste products of a given species were usually 
more toxic to that and closely related species than to those species 
more distantly related. 
Eijkman’s results are confirmed by the recent work of Rahn 
(’06) on other bacteria. Rahn finds a thermolabile toxic substance 
which is absorbed by freshly heated clay filters so that a piece of 
recently heated clay saturated with old bouillon was quickly cov- 
ered by a growth of organisms. The toxic substance was also 
destroyed by diffuse light. 
The work of Emmerlich and Loew (99) and other investigators 
on the action of bacteriolytic ferments and their toxic action on the 
bacteria of many infectious diseases, involving the preparation of 
antitoxins and their use in medicine, is of the greatest interest in 
this connection as showing that the products of bacterial life are 
Poisonous to the living forms of a similar or related species. 
Experimenters upon chemotropism have found that the growth 
of fungus hyphae is not always in the direction of nutrient ma- 
terials, but they will sometimes grow into toxic substances, Clark 
(02) found that the hyphae of Rhizopus would grow from a layer 
of rich nutrient agar into a layer of non-nutrient agar containing 
0.005V copper sulphate. Fulton (06) working on the same sub- 
ject has clearly demonstrated that the hyphae grow in any direc- 
tion that will carry them out of a region already occupied by 
numbers of hyphae. He showed that the repelling substance 
remains in the solution in which the fungi have grown, and that it 
is not carbon dioxide. The results of the two last-named authors 
agree in indicating that the fungus hyphae are negatively chemo- 
tropic to some substances which they secrete and this negative 
chemotropism is much greater than any positive chemotropism 
they may have for nutrients or oxygen. 
According to Ferguson (02) the germination of certain mush- 
oom spores is greatly facilitated when a small bit of living mush- 
oom tissue is included in the culture, but the further development 
of hyphae from these spores is almost completely inhibited. When 
the spores which have been germinated are transferred to cultures 
in which there are no pieces of tissue a continuous development of 
hyphae takes place. This observation would seem to indicate that 
the pieces ot living tissue exerted some influence which inhibited 
