Dixon and Atkins — Osmotic Pressures in Plants. 



431 



A similar objeotion was found to apply to the use of chloroform. For 

 this test samples A aud B were prepared iu the same way as in the foregoing 

 experiment. A was then exposed to the vapour of chloroform for thirty 

 minutes, pressed, aud to the sap obtained a few drops of chloroform were 

 added to ensure saturation. The freeziug-point was then determined in the 

 usual way, except that the control-tube of the apparatus was cliarged with 

 distilled water, saturated with chloroform instead of with pure water. This 

 change was, of course, not made when working with sample B, which before 

 passing had been immersed in liquid air. The conductivities were determined 

 iu the usual manner described iu the paper which follows. 



Hedera Helix : leaves from S. aspect. 



Here again it appears that the exposure to cliloroform vapour has not been 

 sufficient, and it is evidently inadvisable to prolong the opportunity for 

 spontaneous changes beyond thirty minutes. 



The realization that the fluid pressed from untreated tissues does not give 

 a fair measure of the concentration of the sap in the vacuoles of the uninjured 

 tissues must modify the estimates of the freezing-points and the osmotic 

 pressures in the vacuoles of vegetable cells determined by ourselves and others 

 on these juices. In every case we have as yet examined the estimate must be 

 raised, and in some cases very considerably. This may be seen by reference to 

 the table given above. The difference is exceptionally marked in the case of 

 Chamaerops humilis. So far, however, as we have been able to cheek our 

 previous results, we have found that the concentrations of the sap in the 

 various organs of the same plant pressed after exposure to ■ liquid air follow 

 the same order as we found for the sap from the untreated organs, e.g. — 



' The figures given in this column fire the means obtained 'in these series of exp.erimepts recorded 

 in a previous paper (Dixon and Atkins, 13). 



