CH. xxi] TRANSPIRATION STREAM 261 



appeared more than half a century ago. It may further be 

 recalled that, as early as 1858, a French botanist 1 concluded, 

 from certain experiments, that the transpiration of a terrestrial 

 plant can continue when it is grown in a saturated atmosphere, 

 and even when the leafy portion is entirely immersed in water. 

 It is also known that emersed water plants transpire very freely 2 . 

 We shall only find it necessary here to refer to a few of the more 

 outstanding of the researches which bear directly upon the 

 transpiration of submerged plants. 



The more modern work on the subject may be said to begin 

 with Sauvageau 3 , to whom we owe so much of our knowledge 

 of aquatics. He used for his experiments detached branches of 

 submerged plants, in which the cut end of the stem had been 

 sealed with cocoa butter, and all the roots had been removed. 

 He found that, even under these circumstances, the shoots 

 could live and prosper and develop fresh buds thus, up to a 

 certain point, justifying the current view that water could be 

 absorbed through the surface of the stem and foliage. He also 

 performed a converse experiment, by means of which he at- 

 tempted to prove that, under normal conditions, a definite trans- 

 piration current, passing upwards to the leaves, occurs in sub- 

 merged plants. The apparatus used is shown in Fig. 162, p. 262. 

 It was essentially a form of potometer, modified for use with a 

 submerged shoot. This experiment, however, as has been pointed 

 out by a more recent worker 4 , is open to the criticism that water 

 may have been passively forced through the plant, owing to the 

 pressure exerted on the cut surface of the stem by the column 

 of water in the small tube. It seems as if some slight modifica- 

 tion of the apparatus might readily be contrived to obviate this 

 difficulty. 



A number of further experiments were devised by Hoch- 

 reutiner 5 , of which the following example may be taken as 



1 Duchartre, P. (1858). 



2 Bokorny, T. (1890) and Otis, C. H. (1914). 



3 Sauvageau, C. (iSgi 1 ). 4 Weinrowsky, P. (1899). 

 5 Hochreutiner, G. (1896). 



