58 



Finally, when the concentration of the toxic agent is still 

 further decreased, the stimulation threshold in the pres- 

 ent sense is passed and normal germination becomes the rule. 

 Livingston-'-^ working with a green alga has present«d 

 a somewhat similar series of responses to chemical stimuli. 

 This writer studied the effect of a large number of nitrates 

 and sulphates on a form of Stigeoclonium , adding different 

 concentrations of the salts to a nutrient mediiom in which 

 the alga was grown. With a dilute nutrient solution, in 

 which the alga had a characteristic filamentous form, its 

 response to stimulation might he considered as of three 

 types. (1) death, (2) change in phenomena of growth, and 

 (3) change in phenomena of reproduction. The response to a 

 high concentration was usually death, while addition of a 

 toxic salt somewhat below the fatal concentration stimul- 

 ated the production of the palmella form, v;ith spherical 

 cells and division occurring in all directions. It is int- 

 eresting that with relatively similar concentrations of tbes 

 salts, (that is at concentrations somewhat lower than those 

 required to inhibit germination) the spores dealt with in 

 the present paper exhibited responses similar to those 

 which Livingston found with his alga; the production of 

 appressoria and swellings in this fungus appears physio- 

 logically similar to the production of the palmella form 



18. Livingston, B. S. , Chemical stimulation of a green 

 alga. Bull. Torr. Eot. Club 32:1-34, 19C5. 



