1906] FULTON—CHEMOTROPISM OF FUNGI 97 
of a large drop; the preparations were then opened, and with a 
sterile needle the small drops were pushed up until their edges came 
in contact with the larger drops. Later observations showed that 
the hyphae of the three fungi grew readily from either medium into 
a similar or a dissimilar medium, and with the same percentage 
of turning. An equal amount of turning toward the agar drops was 
observed in the case of those hyphae which had grown beyond the 
bounds of the larger drops on the moist glass; whether the agar was 
nutrient or non-nutrient seemed immaterial. The turning was 
apparent at a considerable distance from the surface film in so large 
a percentage of cases as to negative the supposition that the physical 
condition of the film has an influence. 
A further test without mechanical separation was made by placing 
small crystals of cane sugar, copper sulfate, oxalic acid, monobasic 
potassium phosphate, and ammonium nitrate in the center of layers 
of non-nutrient gelatin on cover glasses. Spores of Monilia jructi- 
gena, Botrytis vulgaris, Sterigmatocystis nigra, Mucor stolonijer, and 
Monilia sitophila were used; in some instances they were evenly 
distributed in the gelatin, in other instances the gelatin was inocu- 
lated by being touched with the needle at several points varying 
in distance from the crystal. In no case was there any distinct 
turning toward or away from the diffusion center. 
The effect of hyphae upon the direction of growth—CLARK (4) 
explains his results by supposing that the fungus secretes some 
substance to which the growing hyphae are negatively chemotropic. 
While this hypothesis would very well explain his results, he seems 
not to have made it the subject of experimental study. 
It may be reasonably assumed that if a fungus is negatively chemo- 
tropic to its own secretion, the stimulus to turn away from an area 
containing the fungus would, in early stages of growth, be in some 
degree proportional to the amount of mycelium in that area. 
To determine whether the amount of mycelium has an effect, 
inoculations were made with differing numbers of spores; the growth 
was from non-nutrient gelatin and gelatin containing M/4 solution 
of dextrose, and was toward similar as well as different media as 
indicated in Table VI, where the results are given. The direction 
of growth is from the first-named medium to the second. Columns 
