2 74 BOTANICAL GAZETTE [OCTOBER 



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in the stem be active, the source of energy being the cooling 

 of the stem, which would remove the lO^ limitation altogether. | 



Arendt's observations, apparently of ascending currents main- I 



tained by capillarit}^, have not to my knowledge been corrected or 

 explained. It is safe to assume that the plant does not work on 

 a dangerously narrow margin, and lo™ of water in a tree lOO"^ 

 high would leave a proportion of air for which we know no par- 

 allel. But it is idle to take advantage of what we do not know 

 to spin out speculations. 



This is not a satisfactory state in which to leave a subject. 

 But it may still be regarded as something in '* this most nebulous 

 of subjects/' as Darwin calls it, to have pointed out where our 

 theories fail, and where our densest ignorance lies. The rise of 

 water to make good the loss by transpiration is due to the 

 pressure of the atmosphere, or to this and other forces coop- 

 erating with it and regulated by it. Much farther than this we 

 cannot go until there is a physical explanation of the repeated 

 botanical observation of the passage of water between bubble 

 and wall. 



Stanford University, 



California. 



BIBLIOGRAPHY. 



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The absence of anything like a complete and easily accessible bibliogra- 

 phy has been a difficulty in the preparation of this paper, which I have tried 

 to spare for future work. Not only has there been a dearth of reference and \ 



credit to earlier work, and consequently a great deal of republication, but a 

 surprising number of inaccurate references add to the difficulty. From this 

 list of titles I have therefore omitted all those of works which I have been 

 unable to consult and verify in person, excepting a few which it has seemed 

 best to refer to on hearsay ; these appear in brackets- In spite of this limita- 

 tion, the bibliography will hardly be found glaringly incomplete. The few 

 general texts listed contain matter on this subject which might appropriately 

 have been published separately. The few purely physical works included 

 here are to complete references in the body of this paper. 



Arendt, J. J. F., Ueber die Capillar-Activitat der ausseren Integumente 

 einiger Pflanzen. Flora 26:153-162, 1843 ; and Ann. Sci. Nat. Bot, 19: 

 327-334. 1843. 



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