356 BOTANICAL GAZETTE [NOVEMBER 
amount of mycelium occurs in 2 films composed of the same 
medium, no turning results. 
EXPERIMENTS WITH UNSTALED TURNIP JUICE.—After the exist- 
ence of a negative chemotropism of this kind was proved, it became 
easier to search for a possible positive chemotropism. For, without 
going into detail, it was clear, from the fact that the hyphae are 
continually producing a staling substance, that the number of 
spores and the length of the 
hyphae must be considered 
when one is seeking to obtain 
evidence for positive chemo- 
tropism. 
In the experiments with 
agar made with unstaled 
turnip juice, the first definite 
indication of a positive 
chemotropism (working, it is 
true, side by side with the 
negative chemotropism pre- 
viously demonstrated) was 
obtained. The hyphae grew 
Fic. 4.—Germ tubes growing toward much more vigorously in the 
the halen: “staled” turnip juice eh hae turnip juice medium than in 
a See cone. previously been heated 0 fhe sueare, “They Gil aot ee 
too° C.; otherwise conditions are the same . 
as in fig. 3; 80. all cases grow faster; the chief 
difference consisted in the 
thickness of the germ tubes, which were twice or three times as 
thick as those grown in glucose or in cane sugar agar. Probably 
on account of this healthier development they reacted much better 
to chemotropic influences than when grown in the sugars. The agar 
was prepared by mixing equal volumes of turnip juice with 3 per 
cent distilled water agar, thus forming a medium containing 1-5 
per cent agar. Combinations were tried as follows, the amount of 
reaction in each case being given below: 
A c 
Mica plate > __Plain agar _ Turnip juice agar Turnip juice agar 
Turnip juice agar Plain agar Turnip juice agar 
spores +spores -++spores 
Reaction—> ++ 60-90 per cent +100 per cent +100 per cent 
ax 
