200 TRANSPIRATION AND ASCENT OF SAP ch.x 



the cylindrical cells of the leaves is under 0*05 mm., but 

 even in cells having this diameter and having a thickness 

 of wall equal to 0*001 mm. only, it would require a pressure 

 of 100 atm. to tax the cell- wall to its breaking point. 

 Consequently we may take it that the osmotic pressures 

 of the leaves never seriously tax the tensile strength of 

 the cell- walls. 



Literature. 



Dixon, H. H., "The tensile Strength of Cell-walls," Ann. of Botany, 

 L897, vol. xi, p. 585. 



Id., "On the Physics of the Transpiration Current," Notes from the 

 Botanical School of Trinity College, Dublin, vol. i, p. 57. 



Id., "Transpiration and the Ascent of Sap," Progresses Rei Botanicae, 1909, 

 Bd. iii, s. 1. 



Dixon, H. H., and Atkins, W. R. G., "On Osmotic Pressures in Plants ; 

 and on a Thermo-electric Method of Determining Freezing Points," Proc, 

 Roy. Dublin Soc, 1910, vol. xii (N.S.), p. 275. 



Id., " Changes in the Osmotic Pressure of the Sap of the Developing 

 Leaves of Syringa vulgaris " Proc. Boy. Dublin Soc, 1912, vol. xiii (N.S.), 

 p. 219, and Notes from the Botanical School of Trinity College, Dublin, vol. ii, 

 p. 90. 



Id., "Variations in the Osmotic Pressure of the Sap of Ilex aquifolium," 

 Proc. Boy. DuMin Soc, 1912, vol. xiii (N.S.), p. 229, and Notes from, the 

 Botanical School of Trinity College, Dublin, vol. ii, p. 111. 



Id., "Variations in the Osmotic Pressure of the Sap of the Leaves of Heclera 

 helix," Proc Boy. Dublin Soc, 1912, vol. xiii (N.S.), p. 239, and Notes from 

 the Botanical School of Trinity College Dublin, vol. ii, p. 103. 



Id., " Osmotic Pressures in Plants. I. Methods of Extracting Sap from 

 Plant Organs. II. Cryoscopic and Conductivity Measurements on Some 

 Vegetable Saps," Proc. Boy. Dublin Soc, 1913, vol. xiii (N.S.), pp. 422, 434, 

 and Notes from the Botanical School of Trinity College, Dublin, vol. ii, pp. 152, 

 173. 



Pfeffer, W., "Physiology of Plants," Translated by A. J. Ewart (Oxford 

 1903.) 



Renner, <>., " Exi>erimentelle Beitrage zur Kenntniss der Wasserbewe- 

 gung," Flora, 1911, Bd. 103, Hft. 3, 171. 



