354 BOTANICAL GAZETTE 
[NOVEMBER 
possible that even this degree of heat as well as the delay due to 
evaporation may have led to an alteration of the staling substances. 
Table III shows the results of experiments to determine whether 
raising the staled juice agar to the boiling point altered its repellent 
effect (cf. figs. 3 and 4). 
’ TABLE II 
Staled turnip juice agar 
NATURE OF exonanun Mi Plate > 7 ch turnip juice agar 
-++ spores 
. Number 
Ni riod of Av Total number|p 
Temperature | preparations incubation length of — Prt) of hyphae |” oe * 
examined in hours hyphae in « fin waiters: counted 
Staled | juice Naas 7.50 69 21 240 —26 
not heated - 8 = ; aa an 
over 40° é SEAM SS . 75 foie) 9 3 
Staled juice 
fat to 2c ; 57 31 168 +18 
era [ete 8.50 143 23 218 +72 
In this series the staled solution used was 3 weeks old, and, in 
order to dilute it as little as possible, one part of 6 per cent agar 
was added to 3 parts of the staled juice, a rather difficult operation 
in the case where there was no heating above 40° C., owing to the 
fact that at this temperature 6 per cent agar is very close to its 
_ gelatinization point. 
The results show that the repellent substances of the staled 
solution are as a whole, or in part, unstable or volatile in character 
(figs. 3, 4). If they had been entirely destroyed, we should get 
results similar to those described later for C (p. 357), that is, 100 
per cent of turning. It is possible, however, that the heating 
entirely destroyed the repellent substances, and that the smaller 
reaction as compared with the preparations cited is due to the fact 
that most of the substances in turnip juice which induce a positive 
chemotropism have been used up by the fungus which originally 
produced the staled solution. 
In this connection the work of Lutz (7) is of interest. In the 
investigation of the effect of used solutions on spore germination 
and fungous growth, he found that in many cases high temperature 
