364 BOTANICAL GAZETTE [NOVEMBER 
of material around the hole; and again, the time during which the 
stimulus had been acting (since a longer period gives greater oppor- 
tunities for growth) would also affect the result. Bearing all this 
in mind, we nevertheless seem justified in assuming that under the 
conditions of any given experiment the percentage of turning gives 
some measure, although only a very approximate one, of the in- 
tensity of the stimulus or stimuli acting. 
By an inspection of the results, especially as shown in tables IV 
and V, we can thus arrive at some idea of the relative intensity of 
the negative as compared with the positive chemotropic stimulus. 
For if we denote by the percentage effect due to the negatively 
acting staling substances, and by # the percentage effect produced 
by the positive stimulus, we have in A of table IV, using the 
percentage of reaction in the oldest preparations, n—p=43; 
whereas in B we have n+p=g4, taking the two oldest preparations 
here also. Since the hyphae in these two corresponding cases are 
of approximately equal length, and have therefore probably pro- 
duced an essentially equal amount of staling substance, a compari- 
son is legitimate. By eliminating the ’s, we have 2n=137, or 
n=68.5; p will then be 25.5. In other words, in the special con- 
dition of this experiment, the positive chemotropic stimulus exerted 
by the turnip juice has an effect of a little more than one-third that 
of the negative chemotropic stimulus. In a general way these 
figures are corroborated by the results given for C. 
In the same way, applying this method to the results given in 
table V, we may arrange the relative values of the stimuli as shown 
in table VI. 
With the exception of the youngest hyphae, where diffusion 
of the chemotropic substances has hardly begun, or at least the 
hyphae have not yet had time to react to it, the figures are surpris- 
ingly regular, the percentage of the reaction due to the positive 
chemotropic stimulus remaining fairly constant, as would be 
expected. On the other hand, the negative chemotropic stimulus 
constantly increases with the growth of the hyphae and the excre- 
tion of more and more of the negatively chemotropic substances. 
In C of table V we should expect to find a confirmation of these 
deductions, as was shown by C of the turnip juice experiments 
