1916] GRAVES—CHEMOTROPISM IN RHIZOPUS 353 
agar and staled solution were used, in order to obtain a 1.5 per 
cent agar medium. 
Table II gives the results of one series of experiments. In 
preparing the medium for this, care was taken not to heat the staled 
solution above 40° C. 
TABLE II 
Staled t anon epee ee pane 
-+non-viab 
Al 
NATURE OF EXPERIMENT Mica plate > = van gre ne e aga 
+viable s 
“2 Directi f hyphae Total 
. in on of Dyp: 
preparations | incubation | lengeht | lower layer number of | Peresptage 
ned hyphae in «| of ng seg ed reaction 
surface a B Cc D 
eh ee 7 67 28 7137.97 | 21 152 —53 
Ee 8.25 157 39 gt | 87 |152 | 90 420 19 
nee $0) 331 29 45 | 48 | or | 48 232 —26 
* In this — the s ion was not cen’ rifuged, and this accounts for the presence of spores 
in this layer. They were probably ly dead, however, Sager in any case did no’ inate. Their presence may 
or may oot t have had its effect on the result, but it is extremely doubtful whether they influenced it to any 
con marked d, Similar results were obtained in series where the solution had been freed of its spores by 
Ten holes in each preparation were counted. As would be 
expected, the turning away from the holes is most marked in the 
youngest stage, where the hyphae have not yet produced, by their 
own activity, a concentration of staling substance in any way 
comparable to that of the other film. 
In preparing these films, equal volumes of the staled turnip 
juice and 3 per cent distilled water agar had been used. This 
process diluted the staled juice to one-half strength, or, in reality, 
to its original strength before evaporation. One would expect, 
under these conditions, to see an even greater repellent effect than 
the results show. It is very probable, however, and is also indicated 
by the following experiment, that the repellent substances are of an 
unstable or volatile character. Although, in order to avoid any 
chemical change in the substance, at no time in the making of the 
Preparations was the staled juice agar heated above 4o° C., it is 
