1911] CURRENT LITERATURE 77 
mental knowledge of delayed germination. From the physiological side we 
need to know the structures producing the delay, and how they are acted 
upon by the various conditions that will shorten it. GaASSNER mentions two 
classes of seeds favored in their germination by light: the “dunkelharten” 
type, C. ciliata and Ranunculus sceleratus; and those that are not affected by 
a period of darkness, Poa and many others.—WILLIAM CROCKER. 
Osmotic pressure of leaves.—DrIxon and ATKINS" have devised a thermo- 
electric method for determining the freezing points of juices of plants. The 
advantage of the midis sat over BECKMANN’S lies in the fact that the determi- 
nation can be made with 2. 5~5 cc. of liquid instead of 12 cc. or more. The appa- 
ratus was used for sietcmiuing the osmotic pressures of the sap of foliage 
leaves. The osmotic pressure varied with different species and individuals 
under the same conditions, but was constant for an individual under a given 
condition. In an individual of Syringa vulgaris, change of condition brought 
about a change in pressure from 24.58 to 11.58 atmospheres. The amount 
of pressure was not determined by the height of the leaves above the ground, 
nor by the resistance of the conducting tracts supplying the leaves, but in 
every case the osmotic pressure was much greater than the tension of the water 
supply could have been. Variations were attributed in the main to variations 
in carbohydrate and water content. The osmotic pressure of leaves increased 
with insolation, loss of water, and age. The highest osmotic pressure found 
for Syringa vulgaris was 26.87 atmospheres. The authors believe that during 
summer, when sugars are abundant and transpiration great, leaves of Syringa 
may develop a pressure as high as 30-40 atmospheres. The high pressures of 
leaves is quite in contrast to the pressures of roots of the same species. e 
pressures in the roots varies from 4 to 6 atmospheres. These data of course 
furnish support for the cohesion theory of rise of sap. One wonders how closely 
the osmotic pressure of extracted juices corresponds to that of the living cells.— 
WILLIAM CROCKER. 
Oxidation of hydrogen by microorganisms.—NIKLEWSKI’s” full report of 
work, which has been intermittently in progress since 1904, makes an inter- 
esting and valuable contribution. The study includes the isolation of two 
spec r 
distinguishable. Neither of the two species isolated can develop in an oxy- 
ydrogen atmosphere without the company of the other, but when both are 
present under suitable conditions for growth a condensation of the oxyhy- 
drogen gas occurs. If an inorganic nutrient medium is inoculated with 
** Drxon, H. H., and Arxrns, W. R. G., On osmotic pressures in plants; and on a 
thermo-clectric autiiod of determining freezing points. Sci. Proc. Roy. Soc. Dublin 
N.S. 12:275-311. 1910, 
™ NIKLEWSKI, BRONISLAW, Ueber die Wasserstoffoxydation durch eoaiaeacet 
ismen. Jahrb. Wiss. Bot. 48: 113-142. IgIo. 
