﻿19031 CHEMICAL STIMULATION 87 



harmonize with the details of the degrees of dissociation, since 

 dissociation is very nearly complete in fatal concentrations of 

 several poisons (Kahlenberg and True, 1 896). And it fails 

 utterly to explain the rather abrupt change from accelerating to 

 obviously toxic concentrations. This quick change has, from 

 my point of view, a perfect analogue in the plant's thermal rela- 

 tions in the steep fall of the curve of growth above the optimum 

 temperature. Even the ion theory can be overworked. 



If we interpret the action of chemical stimuli on growth as 

 secondary to that on respiration, we are already armed with an 

 explanation of their influence on reproduction. Klebs''^ has 

 shown that the demands of reproduction upon various conditions 

 are more strict than those of growth. This may be regarded as 

 meaning, in part at least, that the balance of available plastic 

 matter must be relatively great, while the sacrifice of matter for 

 energy must be less than is tolerable for growth. The optimum 

 temperature for reproduction w^ould then be sought below that 

 for growth, and a chemical stimulus accelerating growth might 

 inhibit reproduction. From Klebs^^ again, we know that while 

 the optimum for growth of Vaucheria repem is 30° C, the maxi- 



mum for the formation of zoospores (p. 46) and for sexual 



reproduction (p. 112) is about 26"" C. This idea might still 

 be sound, even if it should be shown that the least percepti- 

 ble quantity of a poison interfered with reproduction. Of 

 course I offer this only as a suggestion, and do not overlook 

 the very likely alternative that acceleration of the growth 

 is the factor which in its turn injures the reproduction. Of 

 course, too, there are outside factors which act on the growth 

 quite independently of the respiration. The blue end of the 

 solar spectrum slackens growth, but has no well authenticated 

 direct effect on respiration. In the case of all chemical stimuli, 

 however, so far as they are known at all, I hold it more than 

 probable that their apparent effect on growth is a function of 

 their more direct influence on respiration. 



»*Klebs, G., Einige Ergebnisse der Fortpflanzungs-Physiologie. Ber. Deutsch. 

 Bot Gesells. 18 :(20i)-(2i5). 1900. 



^^Klebs, G., Die Bedingungen der Fortpflanzung bei einigen Algen und Pilzen. 

 Jena. 1896. 



