January 14, 1910] 



SCIENCE 



55 



in which control cultures are grown, the 

 variant being the same distilled water plus 

 the substance under investigation. It is 

 obvious that metabolic processes and con- 

 sequently growth can take place only in 

 such plants or plant parts in which elabo- 

 rated food material is stored. It is equally 

 obvious that the osmotic relations must be 

 disturbed. Besides the lack of chemical 

 balance there is also a lack of physiological 

 balance. Plants under experimentation to 

 determine the effect of chemical stimula- 

 tion should be referred for comparison to 

 those grown under conditions which are as 

 nearly as may be the ones which can be 

 recognized as producing opportunity for 

 what experience shows is the natural 

 morphological development of the organ- 

 ism. The physiologist should no more 

 neglect the morphological aspects of his 

 investigations than should the morpholo- 

 gist the physiological. 



In its restricted sense, then, chemical 

 stimulation may be said to deal with the 

 effects of chemical agents which are not 

 only not necessary, but which may be posi- 

 tively deleterious to the organism— poisons 

 in short. It has been established that 

 many, if not all, classes of substances 

 which exert a toxic action on protoplasm 

 will become stimulatory if presented to the 

 cells in sufficiently small doses. Some- 

 where between an infinitesimally weak so- 

 lution which produces no reaction, to the 

 toxic dose which kills there is a stimulative 

 optimum which gives the maximum of re- 

 action. Experience shows that this is true 

 of widely diffei-ent substances— a poison- 

 ous gas like carbon monoxide, a poisonous 

 metallic salt like copper sulphate, a simple 

 organic compound like chloroform or a 

 more complex one like an alkaloid, all come 

 under this head. The question which con- 

 cerns this paper is not the possible ulti- 

 mate lethal effect of these noisons, but how 



far they may serve to excite the protoplasm 

 to extraordinary activity. The amount re- 

 quired to effect the latter result will natu- 

 rally vary with the substance, certain mild 

 poisons possibly never affecting the plant 

 beyond the stage of stimulating growth, no 

 matter how high a concentration was em- 

 ployed. 



From the work of Raulin and others, it 

 is known that metallic salts in themselves 

 toxic to protoplasm will, if presented to it 

 in minimal doses, accelerate vegetative 

 processes in a variety of plant forms. 

 Certain fungi may be made to develop 

 their vegetative hyphse much more lux- 

 uriantly by the addition to their nutri- 

 ient substratum of quantities as small 

 as .0005 normal of zinc sulphate,, and 

 the increase of dry weight of cell substance 

 produced may exceed by 200 per cent, or 

 more that which is formed by similar cul- 

 tures without -stimulation. Nor is this 

 limited to salts of the heavy metals, nor in- 

 deed to inorganic substances, for organic 

 substances such as glueosides and alka- 

 loids, or even simpler ones like chloroform, 

 produce a similar if not so marked result. 



In the concentration necessary to pro- 

 duce the characteristic reactions there is 

 great diversity. As would be expected, not 

 only are different substances very un- 

 equally stimulatory or toxic, but also the 

 same substance varies greatly in the 

 amount required to stimulate different or- 

 ganisms. Copper sulphate, one of the most 

 violent of poisons to plant protoplasm, 

 does not inhibit the growth of Penicillium 

 until a concentration of nine per cent, is 

 reached, yet the effect of the same salt is 

 so enormously poisonous to many algse 

 that an infinitesimally weak solution will 

 speedily cause death. What is true of the 

 toxic point is true also of the stimulatory 

 optimum. In the attempt to explain such 

 disparities stress has been laid by some on 



