1915] CURRENT LITERATURE 75 
value ever obtained for the cohesion of a liquid. The measurements were 
made with sap containing considerable air in solution, thus approximating 
the conditions in the tracheae. It is estimated that in the highest trees at 
maximum transpiration, the cohesion necessary to raise the sap does not 
exceed 20 atmospheres, a value well within the tensile strength of sap. For 
determining the osmotic pressure of leaf cells, Drxon has used the freezing 
point method. To this end, he and Atkins have improved the current 
methods of extracting plant saps and have developed a thermo-electric method 
of determining the lowering of the freezing point. The essential new feature in 
the extraction of sap is the emersion of the tissue for some time in liquid air. 
This destroys all living semipermeable membranes and allows the solutes to be 
pressed out unrestrictedly with the water. The main advantage claimed for 
the thermo-electric method is the small amount of fluid needed, 2 cc. as against 
the 15-20 cc. for the ordinary Beckman apparatus. This is frequently a 
very important consideration for the plant physiologist. ith the use of 
multiple juncture couples, a opiate of the freezing point by o.o001° C. can 
be measured as against o.001° C. for the Beckman. With the single juncture 
couples, used in the main by Drxon, a lowering of 0.01° C. can be m 
By reducing the size of the Beckman apparatus, BuRIAN and DRUCKER were 
able to measure the lowering of the freezing point of 1.5-2 cc. of solution 
accurately to o.005° C., and DruCKER and SCHREINER by a different method 
were able to measure the freezing point of 0.005 cc. of a solution accurately 
to o.o1° C2 For the needs of the plant physiologist, I am inclined to think 
that the latter methods are more suitable. 
This book is rather more a statement of the extensive and in the main 
extremely important work of the author on the rise of sap than a critical con- 
sideration of the whole literature of the subject. This accounts for chap. vii, 
which presents Drxon’s cumbersome and inaccurate method of determining 
osmotic pressure of cells of the leaf by balancing it against gas pressure; for 
the slight consideration given RENNER’s work, which proves a critical point 
for the cohesion theory, namely the actual existence under certain conditions 
of a stretch of 10-20 atmospheres in the water of the tracheae; for the failure 
to point out that by a very different method RENNER confirmed a law estab- 
lished by Drxon, namely the rate of flow of a water column through a stem is 
Proportional to the push or pull applied to it; and for the absence of the sig- 
nificant data of HaNnic, Firrinc, and others on the osmotic pressure of leaf 
cells 
As yet the existence of a continuous gas-free water column from root to leaf 
under all conditions has not been established. Until this is established, there 
will be a just argument against the cohesion theory of the rise of sap.—W. 
CROCKER. 
* Héser, Physikalischechemie d. Zelle, etc., p. 22. 1914; Biol. Centralbl. 33:99. 
1913. 
