1916] GRAVES—CHEMOTROPISM IN RHIZOPUS 3390 
follow out this line of work, he advanced the hypothesis that 
Rhizopus is ‘‘markedly chemotactic to some secretion of its own 
‘mycelium, and this negative chemotropism is much greater than any 
positive chemotropism it may have for food substances or oxygen.” 
The work of Futton showed a decided advance in that, by 
introducing numerical methods of estimating the direction assumed 
y the hyphae, he placed on a numerical basis what had heretofore 
been more or less a matter of personal judgment. As Poropxo (9) 
has pointed out, in his work on chemotropism in roots, quantitative 
methods in this field must replace the qualitative ones hitherto 
used, if definite results are to be obtained. In startling contrast 
to Mryosut’s results, FuLTon failed to find “the existence of any 
definite chemotropic sensibility to nutrient substances or other 
chemical compounds in solution.” He believed that if positive 
chemotropism in the fungi exists, it is not as marked as turning 
caused by other stimuli. He states: ‘All of the fungi tested show 
a tendency to turn from a region in which hyphae of the same kind 
are growing, toward one destitute of hyphae, or in which the 
hyphae are less abundant. .... This may be regarded as a nega- 
tive reaction to stimuli from chemical substances which owe their 
origin in some way to the growing fungus.” 
These results were so much at variance with MIyosHI’s con- 
clusions that they have been quoted with great reserve by such 
writers as BARNES (4), PRINGSHEIM (10), and Jost (6); and, on 
account of their conflicting nature, a restudy of the whole matter 
seemed imperative. The present work was undertaken, therefore, 
_ in the hope of deciding between the views of MryosHt on the one 
hand and those of Futon and CLarK on the other. 
Material and methods 
Although the main part of the work was carried on chiefly with 
Rhizopus nigricans Ehrenb., preliminary tests were made also with 
Botrytis cinerea Pers. and a Penicillium which, after culture in the 
requisite media, answered most closely to Penicillium no. 24 Thom. 
Eventually the work was confined entirely to Rhizopus because 
its large spores and hyphae make the microscopic examination 
of the preparation easier; the comparatively short time necessary 
