262 



WATER ABSORPTION 



[CH. 



typical. He employed two branches of Potamogeton pectinatus^ 

 L., arranging one of these branches so that its base, to a 

 depth of 2 cms., was immersed in eosin solution, while its 

 summit was in pure water; the second, he placed with its 

 summit in eosin and its base in pure water. After a couple of 

 days, sections of these two shoots were cut at various levels, 

 and it was found that, in the case of the first branch, the eosin 

 had mounted to a height of 1 5 cms. in the main axis, which was 

 itself 20 cms. long, and to 1316 cms. in the lateral branches. 

 P. pectinatus possesses no vessels, but the xylem lacunae had 



water 



a LP 



mercury , 



geLatlae- ' 



indlarubber-- 



water 



cotton-wool 



-- water 



Fig. 162. Diagram illustrating experiment to show^existence of 'transpiration' 

 current in a submerged plant. [Sauvageau, C. (1891^).] 



evidently formed the path for the transpiration current, the cell 

 walls bounding them being alone coloured bright red. In the 

 case of the second branch, only the epidermis was stained, the 

 vascular tissue of the leaves and stem being unaffected. 



Some experiments, similar in principle to those of Hoch- 

 reutiner, but more striking in result, were made some years ago 

 by two Cambridge botanists^. Their work had the advantage of 

 being carried on in situ^ so that the natural environment of the 

 plant was, as far as possible, retained. Potamogeton lucens was 

 1 Thoday, D. and Sykes, M. G. (1909}. 



