1906] FULTON—CHEMOTROPISM OF FUNGI IOI 
sec. 155), the effects seem to be due either to the excretion of a hypo- 
thetical specific substance which furnishes the stimulus, or to changes 
in the relative proportions of oxygen and carbon dioxid through 
respiratory or photosynthetic activities. Since these phenomena 
seem to be analogous in a general way to the above-described turning 
of fungous hyphae, and since the term cytotropism indicates nothing 
as to the exact nature of the ultimate stimulus-substance, this term 
might be found a convenient one for designating the present cases. 
The effect of moisture-—The circumstance that a number of 
preparations in which the culture medium had become evidently 
dry, gave large percentages of turning, suggested that the hyphae 
might react to a hydrotropic stimulus. Layers of agar containing 
spores of several fungi were spread on cover glasses, and sterile 
strips of filter paper were placed in contact with the agar and allowed 
_ to dip into the water of the Van Tieghem cell. The average per- 
centage of turning toward the strips for those spores within a distance 
of 0.35™™ from their edges was 4o per cent. for Penicillium glaucum; 
50 per cent. for Mucor stolonijer, Monilia sitophila, and Sterigmato- 
cystis nigra; 55 per cent. for Mucor mucedo; 57 per cent. for Botrytis 
vulgaris; and 60 per cent. for Monilia jructigena and Sphaeropsis 
malorum. 
The percentages given are less than they would be if a smaller 
area about each strip had been considered; this may be due in part 
to the circumstance that the spores were rather thickly sown, and 
the hyphae from those nearest the strip, being numerous, exerted 
an effective repellent influence on those more distant, causing them 
to grow away from the strip. Notwithstanding this, the evidence 
of positive hydrotropism for these fungi was quite conclusive. 
As a further test, mica plates were cut to fit Van Tieghem cells 
and were perforated; a drop of non-nutrient gelatin was placed on 
each and covered with a perforated plate small enough to fit inside 
the cell; upon this was placed another layer of non-nutrient jelly 
containing the spores; another perforated plate was added, and a 
third layer of gelatin, sterile like the first; the lower surface of this 
was left uncovered. The mica cover was inverted over a cell con- ’ 
taining water, during the time required for the proper growth of 
the fungi, evaporation took place from the now uppermost layer to 
s 
