408 



BOTANICAL GAZETTE 



[may 



two kinds of Spirogyra are different also in respect to the phe- 

 nomena of antagonism, which will be discussed later. 



If a contraction appears only after some hours or days, it is 

 disregarded, as in such long experiments complicating factors are 

 present. Solutions of barium and strontium salts in lower con- 

 centrations than those indicated will not produce the effect in 

 24 hours. With other salts which usually do not produce the effect 



contractions sometimes 

 appear after 3 or 4 hours 

 (or after several days) , but 

 this may be due to other 



than the salts, 

 because in material dying 



agencies 



A 



B 



Fig. 2. 



form 



pyrenoids omitted; A, normal condition; jB, 

 after treatment with BaCl 2 . 



and was found to be sensitive to both barium 



from natural causes cells 

 with contracted chromato- 

 phores are sometimes 



found . 



The material used for 

 this purpose must be fresh 

 and in good condition, or 

 it will lose its sensitiveness 

 and fail to contract when 

 the salts are applied. For 

 example, material was 

 taken at first from a glass 

 jar kept in the greenhouse 



J 



strontium 



Later this material deteriorated because of the increased sunlight 

 and heat of the greenhouse, and did not respond to SrCL. although 

 still responding to BaCl 2 . Still later it became insensitive to BaCL 

 solution, even at the concentration of 0.1 M. The same thing 

 occurred with the small form which grew in a pond. This decrease 

 of sensitiveness seems to be due to some chemical or physical 

 change in the cell when its vitality is injured, which prevents the 

 chromatophores from contracting. 



As this visible effect of barium, strontium,' and cerium is well 

 suited to the study of antagonism, attempts were made to see 

 what salts hinder or prevent these effects. 



