ON THE NATURE OF THE STIMULUS CAUSING THE 



CHANGE OF FORM AND STRUCTURE IN PROS- 

 ERPINACA PALUSTRIS. 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 



XXXVII. 



By William Burnet M c C a l l u m. 



(with ten figures) 



Although heterophylly in amphibious plants has long been 

 a subject of observation and experiment, as yet we are in 

 Ignorance of the real factors that determine which type of leaf 

 such a plant shall assume. The environment of a submerged 

 water plant is certainly a complex one, and there has not been 

 anything like a definite analysis of it. If we are to understand 

 the behavior of a plant when submerged, it is clear that there 



must be a definite knowledge of the various factors concerned, 



and of the influence of each one upon the plant. The literature 



on the subject in the main discusses such topics as water medium, 



diminished light relations, different oxygen and carbon dioxide 



conditions, buoyancy, nutrition, and the like; but such terms are 



general and indefinite, and convey little real information as to 



the actual factors acting upon the primordial cells of the plant. 



The demands of physiology can only be satisfied by a detailed 



analysis of all the possible factors, each of which is a complex 



' in itself, and a determination of the direct action of each resolved 



component upon the protoplasm of those portions of the plant 



involved. ^ Of course such an aim is only ideal and at present 



cannot be realized, but it is, nevertheless, the ultimate goal to 



be reached, before we can read the plant in terms of its envi- 

 ronment. 



In the hope of obtaining some Information upon this question, 

 experiments were begun on Proserpinaca palustris in the autumn 

 of 1900, and are still in progress. The plants used have been 

 grown from seed or obtained from the low-lying lands about 



1902] 



93 



