Transpiration and the Ascent of Sap. 29 



conclude that the absorption and the elevation of the sap are caused 

 hy capillarity. He found that the experiment mig'ht be repeated with 

 leafy branches of various trees and especially conifers.^) From this 

 he draws the extraordinary conclusion, that conifers possess vessels 

 in which the sap ascends. He further states, without giving- reasons, 

 that osmotic actions are not concerned with the supply of the parenchy- 

 matous cells of the leaf, but that this is kept up by atmosphei-ic 

 pressure. 



In 1890 Böhm'-) reaffirmed these convictions, and he states 

 that the experiment described above shows that the capillary attraction 

 of veg-etable vessels compared with glass tubes of the same diameter 

 is incomparably g^reat (unverhältnissmässig g-ross) and that in plants 

 there are continuous (though intersected with cell-walls) filaments of 

 water. The hydrostatic pressure of these water columns is removed 

 by friction. He considers, harking back to the air-pressure theory, 

 that local movements are decided by pressure differences in the bubbles. 

 Notwithstanding his statement that the water filaments are intersected 

 bj^ cell- walls (von Zellwänden durchquerte Wasserfäden), he goes on 

 to say that, if the conifers were without vessels, it is self-evident 

 that the water could not be drawn in by them. The fact that 

 branches of conifers draw up water renders, for Böhm, the denial 

 of coniferous vessels, i. e. series of tracheids, the members of which 

 are in open communication with one another, simply absurd.'^) 



In his summary he reiterates the statement that the sucking up 

 of water through the roots and the ascent of sap is a capillary 

 function of the vessels. He also considers the weight of the water- 

 columns removed by friction. 



B ohm's last paper appeared in 1893.'^) It is chiefly occupied 

 with a reply to criticisms on his hypothesis, which he summarizes as 

 follows: „dass die Wasseraufnahme und das Saftsteigen durch Capil- 

 larität bewirkt wird und daß die Oberhaut und Mesophyllzellen als 

 elastische Bläschen ihren Wasserverlust durch einfache Saugung aus 

 den Gefäßbündeln decken". He then proceeds to describe several 

 very interesting experiments which are the „Treffer" out of a 

 very large number. In these he succeeded, by very careful exclusion 

 of undissolved air, to cause transpiring branches to draw up mercury 

 in a narrow tube not only to, but beyond, the barometric height, — in 

 one case up to 906 cm. In the light of our present knowledge of 



*) J. Böhm, loc. cit., 55. 



') Idem, Ursache der Wasserbewegung in transpirirenden Pflanzen. Verh. d. 

 k. k. zoologisch-botanischen Gesell, in Wien, 1890, p. 149. 



') J. Böhm, loc. cit., pp. 156 and 157. 



^) J. Böhm, Capillarität und Saftsteigen. Ber. d. Deutsch. Bot. Gesell., 11. 

 1893, p. 203. 



