328 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



and C the turning in all cases was lOO per cent., while in A it 

 varied from 60 to 90 per cent. 



In C, since the turnip juice was everywhere of practically the 

 same concentration, the only force exerted must be due to the 

 staling substances produced by the hyphae, i. e., a negative chemo- 

 tropic force. In B, however, where we have the most marked 

 turning of all, we can fairly assert that the turnip-juice agar in 

 the sporeless layer is the cause of the additional stimulus, and 

 exerts, therefore, a positive chemotropic stimulus; in other words, 

 in this case the positive and negative forces are working together. 

 This is borne out by the condition in A, where in the lower layer 

 the positive chemotropic force is working against the negative 

 chemotropic force, with the resulting decrease in the percentage 

 of hyphae reacting. 



Since the existence of a positive chemotropic stimulus was thus 

 established, the next point was to determine the relative strengths 

 of the two stimuli. In the above experiments, the hyphae had 

 been allowed to grow to a considerable length, none being under 

 300 jx, and it was reasoned that with long hyphae the negative 

 chemotropic stimulus would be much greater than with short 

 ones. On the other hand, the positive chemotropic force should 

 be exerted just as strongly on short hyphae as on long ones. In 

 view of this, younger stages were examined, with results such as 

 set forth in the following table. The arrangement of data is as 



in TABLE I. 



Table II 



Nature of preparation 



Per cent of reaction 



at dYi hrs. from 



sowing 



Per cent of re- 

 action at j% 

 hrs. from sow- 

 ing 



Per cent of re- 

 action at 8 J 

 hrs. from 

 sowing: 



Total no. of 

 hypiiae ex- 

 amined 



I'lain agar 



Turnip-juice agar 

 + spores 



+ 



+ 18 



+ 43 



468 



E* 



'ruriiip-juicc ai^ar 

 J'laiii a^ar + sfK)rcs 



riirnip-jiiicL- a^ar 



-j- spores 



I'laiii agar + spores 



Turnip-juice agar 



+ spores 

 Ttirnip-juire agar 



+ s|)ori'S 



- 6.7 



1228 



1 + and — signs indicate positive and negative clK'niotro])ic reaction respectively. 

 * Examined at 7 and 7 J hours after sowing. 



