BIOLOGICAL PAPERS. 115 



Mr. Chamberlain. — "Every dome, at the time it is produced, is 

 the apex of the plant, and that passes down, with very complex 

 anastomosing into those of the leaf traces. It is, therefore, re- 

 lated directly to one of the cylinders." 



DEMOXSTRATIOX OF THE MOVEMENT OF THE 

 WATER IN LEAVES. 



By Aaron Hobgmax Cole. 

 Chicago Teachers' College. Chicago. 



(Abstract.) 



A brief statement of the present state of knowledge of trans- 

 piration in plants will furnish an appropriate setting for the 

 demonstration of the moving stream of water as it traverses the 

 veins of leaves. \\'e have not seen a clearer statement than that 

 of Dr. C. R. Barnes in his admirable '"Physiology of Plants,"* 

 from which we quote as follows : 



''The ultimate cause of the ascent of sap is transpiration ; but 

 how it acts is entirely unknown."' 



"The evidence that the xylem is the path of the transpiration 

 stream rests in part upon direct observation, but mainly upon 

 inference from the eflfects of cutting the xylem strands or block- 

 ing the tracheae." 



"It is fairly certain that the transpiration stream traverses the 

 xylem strands and that it is the lumina of the tracheae that form 

 the conduits for the water." 



"The xylem strands form a connected series, extending from 

 the root-hair region to the mesophyll of the leaves, among which 

 they branch so extensively that there is scarcely a cell which is 

 separated from a strand by more than a half dozen of its neigh- 

 bors. Here the first branches end blindly or join their fellows." 



It is my purpose to demonstrate briefly a method which I have 

 recently developed for making visible to the eye, either without 

 or with the aid of magnification, the actual movement of the 

 transpiration stream along the xylem strands of live leaves. My 

 investigation was undertaken in the hope that my students might 

 see the movement of the sap when demonstrated with a projec- 

 tion microscope or by direct observation. The use of translucent 

 plant stems and modified leaves gave negative or unsatisfactory 



*Te-xt Book of Botanv, (Coulter, Barnes and Cowles) pp. 351, 347, 348, 342 

 and 343. 



