IV.] VARIOUS THEORIES, &C. 133 



Less obvious, but important, points are the radial 

 elongation of the medullary ray-cell, in order to cover 

 several tracheides the fine air-canals which run be- 

 tween the cortical and medullary ray-cells, and thus 

 lead from the lenticels the simple pits which enable 

 the cells of medullary rays to communicate with these 

 air-channels and with one another, and so on. 



Godlewski then passes to the consideration of 

 Westermaier's theory of " clambering," pointing out 

 that however similar they may appear, the two views 

 differ greatly in detail. 



In the first place Westermaier regards the wood- 

 parenchyma as furnishing the path for the movement, 

 as well as the moving forces. He also makes no use 

 of transpiration, and his view would only account for 

 very slow movements ; moreover the hypothesis would 

 not apply to the Pines and Firs. 



As regards Scheit's views, Godlewski points out 

 that he stands alone in denying (without proving) that 

 no air exists in the tracheal elements : as pointed out 

 over and over again, the water passing in at the roots 

 has air dissolved in it, and even if all else is used up 

 there will be nitrogen gas in the bubbles. 



In 1885, Kohl published the results of some experi- 

 ments 1 bearing on Dufour's statements. He showed 



1 " Zur Wasserleitungsfrage," Bot. Zeit. 1885, p. 522. 



