578 SCIENCE PROGRESS 



and Stiles and Jorgensen is not surprising, as the swelling or 

 shrinkage depends among obvious factors on the resistance to 

 stretching of the cell wall, the passage of water through the 

 protoplast, the passage of water through the cell wall, and 

 on the previous history of the tissue. Under these circum- 

 stances it is obvious that conclusions drawn from temperature 

 coefficients should be made with extreme caution. 



Permeability to Dissolved Substances: (a) Seed- Coats. — 

 A. J. Brown and F. Tinker (Proc. Roy. Soc. B, 89, 373-9, 191 6) 

 have continued their investigations on the permeability of the 

 seed-coat of barley. Seeds were steeped in solutions of aniline, 

 phenol and acetic acid, and the extent of absorption of these 

 substances determined by direct analysis of the seeds. With 

 aniline and phenol the substance accumulates in the seed to 

 such an extent that the solution inside the seed is about three 

 times as strong as that outside. Acetic acid, on the other 

 hand, is not " heaped up " to the same extent, and for stronger 

 solutions (the ratio acetic acid : water between 0*5 and 0*9) 

 the strength of solution inside the seed remains constant at 

 80 per cent. 



(b) Living Tissue. — A valuable criticism of the plasmolytic 

 method used for permeability estimations has been offered by 

 Fitting (Jahrb. f. wiss. Bot. 57, 553-612, 191 7). It has previously 

 been generally assumed that a determination of the perme- 

 ability of the cell can be obtained from the differences between 

 isotonic coefficients as determined plasmolytically and the same 

 coefficients determined physico-chemically. If a substance is 

 impermeable these values should be the same ; if it is per- 

 meable the plasmolytically determined isotonic coefficient should 

 be higher. Fitting points out that earlier determinations of 

 isotonic coefficients by the plasmolytic method were subjected 

 to various sources of error in that (1) no account was taken 

 of exosmosis from the cells, (2) the relation between plasmolysis 

 and time was neglected, (3) the gradations between the salt 

 solutions used were not sufficiently fine, (4) the coefficients 

 were determined in relation to potassium nitrate instead of 

 sucrose, and (5) salt solutions may have a possible influence 

 on permeability. Among possible errors in the physico- 

 chemical determination of isotonic coefficients the assumption 

 that the van 't Hoff law holds for the concentrations used is 

 likely to be of importance. The general conclusion is drawn 



