1909.] NATURAL SCIENCES OF PHILADELPHIA. 



101 



that response is not arrested until the poison has actually penetrated 

 and killed the living cells, thus putting a stop to the suctional activity 

 and responsive power of the living cells. The poisons enumerated, 

 being perhaps more easily conducted, act at once in killing the cells, 

 which with other poisons are stimulated long before they are eventually 

 killed. Bose (loc. cit, 383) has demonstrated this differential activity 

 of poisonous solutions in a number of his experiments. Among various 

 solutions of salt, some are physiologically neutral in their effects; of 

 these potassium nitrate may be taken as an example. Others, again, 

 like a strong solution of sodium chloride, act as excitatory agents. 

 The application of this last reagent is known to initiate rhythmic 

 excitation in animal tissues. Similar effects have been shown to be 

 brought about by this reagent in the case of Biophytum and Desmo- 

 dium. Thus in a strong solution of potassium nitrate we have a 

 reagent whose physiologic action is more or less neutral, while its 

 osmotic action is pronounced, and in a strong solution of common salt 

 we have an agent which is both excitatory and osmotic at the same 

 time. If, then, we apply K NO 3 solution to the base of a cut stem, 

 placed in the shoshungraph (Bose's apparatus), water will be osmotic- 

 ally withdrawn from the plant in opposition to normal suction, and 

 the normal suctional rate will be somewhat reduced. On the appli- 

 cation of copper sulphate, the suctional movement, Bose found, was 

 quickly arrested, and this was followed almost immediately by a slight 

 movement in the negative direction ; showing that by some spasmodic 

 contraction water was expelled from the tissue. This phase was 

 succeeded by an almost complete arrest of suction, there being now 

 only the feeblest ascensional movement. Within a short period after 

 this, on washing off the poisonous reagent, it was found that the arrest 

 had been temporary only, suction being renewed at the rate of eleven 

 instead of the normal fifteen cubic mm. per minute. The poison was 

 applied once more and allowed to act for thirty-six hours. The arrest 

 was then found to be permanent — that is to say, the substitution of 

 fresh water induced no revival of response, the plant being killed 

 throughout. It is interesting to note that the twigs experimented 

 with at the University of Pennsylvania responded after a much longer 

 time interval than thirty-six hours, as noted in the experimental data 

 above. 



It will be noted also that the sequence between northern and south- 

 ern grown twigs was preserved in the experimental liquids. If the 

 results obtained in the chemical solutions are contrasted with those 

 in the water, it will be found that the buds on branches obtained from 



