1916] GRAVES—CHEMOTROPISM IN RHIZOPUS 355 
(80-100°) destroyed the effect of these solutions, or at least tempo- 
rarily altered it. Furthermore, he remarks, ‘Wenn sich zeigen 
lisst dass die uns interessierenden Stoffe durch Kochen zerstért 
werden, so liegt die Annahme nahe dass es sich bei ihnen vielleicht 
um fermentihnliche Kérper handelt”’ (7, p. 106). 
The theory advanced by CLarxK and Futton, therefore, that 
during their growth the hyphae produce some substance or sub- 
eee 
i) 
S 
Fic. 3. Plectin —— of aeeiredore nigricans growing away from the hole; film on 
the other sid “‘staled’”’ turnip juice; hyphae are growing 
in a medium composed of unstaled turnip. juice agar; X80 
stances to which they are negatively chemotropic, is fully proven 
by the present work, being supported by 3 lines of evidence: (1) the 
hyphae turn away from a film without spores if it contains their 
own staling substances; (2) the hyphae always show a marked 
turning from their own medium to a second one without hyphae, 
no matter what the constitution of either medium may be, unless, 
Indeed, the second medium contains substances which exert a 
negative chemotropic stimulus; (3) when an approximately equal 
