Contributions to the History of Dionsea Hus= 



cipula, Ellis. 



By J. M. Macfarlane, D.Sc. 



(WITH PTA TE IV.) 



IT is not surprising that a voluminous literature already 

 exists regarding Dioncea. The movements and digestive- 

 action of the leaf as studied specially by Darwin and T. A. 

 G. Balfour, coupled with the electrical conditions shown to 

 exist by Burdon Sanderson have invested the plant with more 

 than ordinary interest. But while Darwin harmonized the re- 

 lation of the plant to others that catch and digest insects, the 

 interest excited by this seems to have prevented his reaching 

 some of the more striking phenomena. And similarly Burdon 

 Sanderson, concerned mainly with electrical action, has not 

 followed out many of the suggestive lines which he touched. 

 Six years ago, while examining some leaves during a warm 

 forenoon in June, I was rather surprised to notice that appar- 

 ently in all cases two touches of the sensitive hairs were 

 needed to effect closure. This observation, often verified dur- 

 ing subsequent years, was made in forgetfulness of Sanderson 

 and Page's statement : " If one of the sensitive hairs of a 

 leaf" .... " is carelessly touched {i. e., when full open) 

 the leaf usually closes. If, however, a hair is touched very 

 cautiously, with the aid of a camel's hair pencil, it can be pre- 

 dicted with certainty that no visible effect will be produced, 

 and a similar gentle contact maybe repeated several times be- 

 fore the leaf begins to answer to the irritation by any move- 

 ment." The writer was led, however, to a closer study of 

 the plant, and the results now given are the outcome of that 

 study. 

 The subject may best be discussed under the following 



