1 88 TRANSPIRATION AND ASCENT OF SAP ch. 



Here again it appears that the exposure to chloroform 

 vapour has not been sufficient, and it is evidently inad- 

 visable to prolong the opportunity for spontaneous changes 

 beyond thirty minutes. 



It appears from the experimental work detailed in this 

 chapter that the liquid pressed from untreated vegetable 

 tissues is not an average sample of the sap contained in 

 the cells of those tissues. However, exposure to intense 

 cold, as may be conveniently effected by treatment with 

 liquid air, renders the cells permeable and secures that 

 the sap yielded up under pressure is not altered in concen- 

 tration during its passage from the cells. Exposure to 

 heat, toluene or chloroform vapour cannot be recom- 

 mended for securing this end. 



Literature. 



Andre, (i., " Sur la composition des liquides qui circulent dans le vegetal," 

 Gompt. rend., 1906, 142, p. 106. 



Id., "Sur la composition des sues vegetaux extraifcs des racines," Gompt. 

 rend., 1906, 143, p. 972. 



Id., "Sur la composition des sues vegetaux extraits des tiges et des 

 feuilles," Gompt. rend., 1907, 144, p. 276. 



Id., " Sur la migration des principes solubles dans le vegetal," Gompt. 

 rend., 1907, 144, p. 383. 



Atkins. YV. R. <;., " Cryoscopic Determinations of the Osmotic Pressures 

 of some Plant Organs," Proc. U(j. Dublin Soc, 1910, vol. xii. (N. S.), p. 463, 

 and Notes from the Botanical School of Trinity College, Dublin, vol. ii, p. 84. 



Dixon, II 11., and Atkins W. R. G., " On < >smotic 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., "Osmotic Pressures in Plants. I. Methods of Extracting Sap from 



