1916] GRAVES—CHEMOTROPISM IN RHIZOPUS 365 
(table IV), but we have already seen why there is a discrepancy in 
the results for the lower film. On the other hand, the —19 per 
cent in the upper film is not greatly in excess of the amount repre- 
senting the positive stimulus in A and B, for since the sugar in 
this case is in the upper film, the stimulus resulting from this would 
attract the hyphae away from the holes, and thus cause a negative 
figure. 
TABLE VI 
RELATIVE VALUES FOR POSITIVE AND NEGATIVE CHEMOTROPIC STIMULI IN CANE SUGAR 
EXPERIMENTS 
Percen Percenta: 
Average length of Nature of Percentage of total * : 
Solas | gush, (POE SS of ction tof ation st 
* 
i ae 2 | Gram { . eS : } } (— 4.0) (+ 2.0) 
Sap-tee? { . fe } +14.0 +23.0. 
ced ae Eee { 5 nao} \ +11.5 +23.5 
Tine, eee { 3 ae } +11.5 +43.5 
Very longt....... { 2 Bh \ +11.0 +60.0 
2 Phe reenltc in h , eee 1 £243) ee p *. res | : 
t These fig Ps £ eh : Poe i : ts, a Ae a ¥ 
- 
COMPARISON OF THE CHEMOTROPIC STIMULUS CAUSED BY CANE 
SUGAR AND BY TURNIP JUICE.—The cane sugar medium of 5 per 
cent’ strength, which seemed to be the proportion most favorable 
for growth, exerts, therefore, a comparatively small positive chemo- 
tropic force. Since it has been shown that when the turning is not 
very marked, the counting tends to be about ro per cent too low, 
these numbers should probably be increased by about that per- 
centage. But even if this be done, in comparison with it the 
stronger positive chemotropic force manifested by turnip juice 
is extremely striking and suggestive in relation to problems 
of parasitism, since it may indicate that plant juices in general 
evoke a fairly high positive chemotropic response. 
