CYTOLOGIOAL CHANGES PRODUCED IN DROSERA. 221 



cell constituent directly influenced by external stimuli^ and 

 that nuclear changes are the secondary results of metabolism. 

 A careful comparison of the action of the substances applied 

 to the tentacles proves that there is a constant concord between 

 the rate of closure of the tentacles and the degree of vacuola- 

 tion produced in the cytoplasm. The citation of a few cases 

 will illustrate this : 



Paraffin and nuclein caused no closure, and very slight and 

 transient vacuolation. 



Pure peptone caused very slow inbending, and no vacuolation 

 for one or two hours. 



White of egg and milk caused rapid bending and rapid 

 vacuolation. 



Fibrin caused slower closure and slower vacuolation. 



Creatin did not induce bending of all of the tentacles to 

 which it was applied ; and those that closed did so with extreme 

 slowness. The vacuolation was only transient. 



Leucin sometimes, but not invariably, occasioned bending, 

 and this was extremely slow. Vacuolation of short duration 

 ensued. 



Urea caused no bending, but killed the leaves. Being 

 therefore a poison, its action should not be compared with that 

 of the other stimulants named. 



5. By bringing healthy cells into contact with the waste 

 products, creatin, leucin, and urea, urea was found to act as a 

 poison, creatin as a mild stimulus to movement, and leucin 

 caused active secretion without much movement. These two 

 substances, therefore, do not injure the leaves, and they seem to 

 be of some nutritive value. 



At a future time I may ascertain the effects of feeding with 

 various carbohydrates, should the results obtained from 

 preliminary experiments give promise that such an investiga- 

 tion would be of any value. 



In conclusion I desire to acknowledge the kindness of 

 Professor Gotch in allowing me to work in the Physiological 

 Laboratory at Oxford, and to express my indebtedness to 

 Dr. Gustav Mann for his constant advice and help. 



