Ii8 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



takes place, contain no chlorophyll-corpuscles, and 

 therefore cannot produce osmotically active sub- 

 stances. 



(3) If osmosis replaces the transpired water why do 

 not plants become filled to overflowing when placed 

 in a damp atmosphere ? 



(4) Green plants placed in the dark for some time 

 ought to use up all their osmotic substances, and 

 would then droop if placed again in the light, whereas 

 they do not do so. 



(5) If the movements of water in transpiring leaves 

 is due to osmosis, then so is that in the stem of those 

 plants which have " parenchymatous wood." 



To which Godlewski replies as follows : 



(1) Movements due to osmosis are slow, it is true, 

 but the distances traversed are very minute, and the 

 fine network of vascular bundles in the leaf is so 

 arranged that no particle of water need have to 

 traverse more than two or three cells. 



(2) If we had to assume that no osmosis could occur 

 except at the spots where osmotically active substances 

 are produced, it would follow that no colourless cells 

 can become turgescent a conclusion falsified by all 

 we know of the cells of pith, roots, parasites, &c. 

 Moreover, Boehm is wrong in ascribing transpira- 

 tion so expressly to the epidermis cells : it is the 



