1922] CURRENT LITERATURE 421 
portion is called “‘free’’ water, to distinguish i it from the mane ae : 
water. The portion of the latter capable of b 
adsorbed, while that which does not freeze at all i is the combined water or the 
water of solid solution and of hydration 
The physiological and ecological signtiiéizice of such a classification is 
indicated by showing that a close relationship exists between the unfree water 
and the wilting coefficient of BricGcs and SHANTz, and between the combined 
concisely expressed as — gravitational water being the same as in older 
systems of classificatio 
t.. Gravitational oo se ose 6 a ee haga 
Be PCO Ree ea at ese suey Ceca ao eey vaila 
Capillary-adsorbed: . 5 oss «2160 waein slightly svallehle 
3. Unfree water of solid solution | 
Combined { water of hydration proses unavailable 
The method of measuring the relative amounts of these various forms of 
water in the soil is known as the dilatometer method, and is relatively simple, 
being based upon the expansion of water upon freezing. This method wo 
also seem to offer a convenient, rapid, and accurate method of determining 
the wilting coefficient.—Gro. D. FULLER. 
Nutrients for Rhizopus.—Miss Dunn’ has studied the effect of various con- 
centrations and proportions of nutrients upon BLAKESLEE’s two races (male and 
female) of Rhizopus nigricans. The salts KH,PO,, NH,NO;, MgSO,, and FePO. 
were used in various proportions, and total concentration with glucose or glycer- 
ine as the carbon source. Apparently calcium is not needed by this plant, 
and it makes no use of nitrate as a nitrogen source, but uses the NH, ion. 
Under the conditions of this investigation “the activity of the organisms 
appears clearly to be controlled by a combination of (a) salt proportions (or 
perhaps ion proportions), (b) total salt concentration, and (c) dextrose con- 
centration. When these three conditions are poorly balanced for the growth 
of these races, the solution may sometimes be greatly improved by altering 
just one of the conditions, but it is frequently necessary to alter two conditions 
simultaneously to obtain good physiological balance. The solution repre- 
Senting the best combination has the following characteristics: (2) Molecular 
salt proportions: KH,PO, 6.0: NH,;NO,1.0 : MgSO,1.1 : FePO, a mere trace. 
(6) Total salt concentration, equivalent to a calculated osmotic value of 14.5 
atmospheres. (c) Dextrose concentration, 1.0 gram-mol. per liter.” There 
was no consistent difference in dry weight production between the male and 
female races when grown on dextrose, but when grown with glycerine as the 
N, Grace A., A comparative study of the two races of Rhizopus nigricans. 
Physiol Researches 2:301-339. 1921. 
