Current Literature 479 



Kttle or no ascent of eosin in the stem. Under these conditions, 

 it would seem that the rise of eosin in the branch was due to secre- 

 tory action of the protoplasm and not to evaporation from the 

 leaf surfaces. 



In regard to the causes of the ascent of water in stems, the author 

 dismisses the various gas-pressure theories with the statement that 

 either the conditions postulated do not exist in the stems, or if 

 they do exist, the proffered explanations of them will not stand 

 the test of physical laws. He reinvestigated, with numerous care- 

 ful experiments, Sachs' theory that the water of the transpiration 

 stream travels in the walls of the conducting tubes, not in their 

 cavities, and he confirmed the conclusions of earlier investigators, 

 that, while some water did pass upward in this manner, the quan- 

 tity was not sufficient to meet the requirements of leaf evaporation. 

 The various theories based upon the assumption that living cells 

 of the wood, either the wood parenchyma or the medullary rays 

 or both, furnish the effective forces for lifting the water, become 

 untenable as the result of experiments which demonstrate that 

 when such cells are killed, the water continues to ascend. Such 

 experiments have been performed at intervals for the past 100 

 years, yet the vitalistic theories cling to life with great tenacity. 

 They have been rejuvenated with considerable vigor within the 

 past decade by Ewart and Urspring. In killing the stems with 

 steam, they found that the rapidity of leaf wilting above the killed 

 portion was dependent upon the length of the killed portion: the 

 longer, the quicker the leaves wilted. Therefore, they argued that 

 living cells were necessary to supply the leaves with sufficient water. 

 Dixon repeated these experiments and got similar results, but his 

 interpretation of them was different. He found that as a result of 

 the disorganization and decomposition of the cells subjected to 

 steam, poisonous substances were produced and these carried to 

 the living cells of the leaf produced their death, hence the leaves 

 wilted and died. When a zone of a stem is killed without the 

 disorganization of the cells, as for example, by a jacket of hot 

 wax, the poisonous substances are not produced and such treat- 

 ment does not interfere with the passage of water. Also when the 

 contaminated steam-killed portions are flushed out by injecting 

 water through them, the leaves did not wilt more readily than in 

 the control experiment. Therefore, Dixon believes that living 

 cells of the wood are not necessary for the ascent of water in stems. 



