412 Canadian Record of Science 



the nature of the stimulus. That there must be a 

 stimulus of some sort is evident, but it seems to be 

 rather the sensitiveness of the organism than the 

 nature of the stimulus which determines the degree of 

 the response. 



The stimulus, both in Borge's culture media and in 

 drop-cultures, was very probably the same, namely, a 

 certain amount of irritation due to contact. In my cul- 

 tures, the stimulus was apparently due to irritation 

 caused by contact with other forms in a crowded 

 aquarium, this being sufficient to produce marked rhizoid 

 formation in the highly sensitive 8. fluviatilis. In the 

 second place, it may be suggested that this sensitive- 

 ness among certain species of algse, which expresses 

 itself in a more or less strongly marked tendency to 

 form rhizoids, may have some connection with the 

 thigmatropism shown by some of the higher plants. 



This view is in harmony with the results of Prof. 

 Derick's study of the early development of many of 

 the red algae 5 . In them the stimulus determining 

 the point of origin of holdfasts and rhizoids seemed to 

 her to be undoubtedly that supplied by contact irri- 

 tation. 



Systematic List. 



I. Chlorophyceae. 



Order I. Conjugatae. 

 Family 1. Desmidiaceae. 

 Closterium Jenneri, Ralfs. 



Crescent shaped, small, slightly tapering, six to 

 eight times longer than broad, ends obtusely 

 rounded, vacuole large, containing many active 

 granules, cell wall colorless, smooth- Diam. 

 about 14 micr. 

 Verdun, Bout de l'lle, Amherst Park. 



