1906] FULTON—CHEMOTROPISM OF FUNGI 83 
spores and from the conidia of Peronosporaceae, and of chemotaxis 
in the case of Cystopus swarm-spores. 
Many of the foregoing are merely opinions or passing observa- 
tions, made in the course of investigation of other phenomena. 
Mryosur (20), however, made chemotropism of certain fungi the 
subject of systematic and extensive experimental study. The -prin- 
cipal fungi used by him were Mucor stolonijer, M. mucedo, Phy- 
comyces nitens, Penicillium glaucum, Aspergillus niger, and Sapro- 
legnia ferax. The tests were made with the aid of perforated mem- 
branes, such as strips of epidermis, celloidin films, and mica plates; 
of capillary tubes; and of injected leaves and petioles of Tradescantia 
sp. He concludes that, in the case of the fungi enumerated, mole- 
cules of many substances diffusing from the openings cause diversion 
of the hyphae from their original direction of growth, the turning 
being either toward the diffusing substance (positive chemotropism), 
when the substance is attractive to the fungus, or away from the 
substance (negative chemotropism), when the substance is repellent. 
Some substances are wholly or almost wholly neutral. The direc- 
tion and amount of turning are dependent upon the concentration. 
Chemotropism is most marked at an optimum concentration, which 
varies for the substance and the fungus. The concentration just 
sufficient to cause turning is very low for most attractive substances. 
Repellent substances are acids, alkalis, alcohol, certain neutral salts 
and toxic compounds; also very strong solutions of substances that 
are neutral or attractive at lower concentrations. Generally attract- 
ive substances are ammonium nitrate, ammonium chlorid, ammon- 
ium malate, ammonium tartrate, potassium phosphate, sodium 
phosphate, ammonium phosphate, meat extract, peptone, sugar, 
asparagin, etc. For chemotropic phenomena Weber’s law holds. 
The effect of an attractive substance may be overcome by the pres- 
ence, in sufficient quantity, of a repellent substance. 
The same investigator (21), in connection with his study of the 
penetration of natural and artificial membranes by fungi, found that 
the hyphae of Botrytis cinerea and Penicillium glaucum would grow 
through a rhembrane only when they were placed on nutrient substrata; 
there would be, however, no penetration through the membrane to 
