1915] CURRENT LITERATURE 83 
rostratum, and Catherinea undulata, withstood 8-20 weeks in dry air and 5-13 
weeks in the desiccator; and in species from the drier coniferous woods, like 
Bartramia ityphylla, Dicranum fuscescens, and D. scoparium, the resistance to 
dry air extended to 50 weeks and in the desiccator to 40 weeks. It should be 
noted that after all the leaves were thus killed, many of the a were still 
of e 
it leaf cells still alive after 128 weeks of continuous exposure to dry air. Species 
from tree trunks showed resistance of the same order as those from the rocks. 
Field observations show that alternate wetting and rapid drying are more 
detrimental in their effects than continuous drought; also, that the same 
species growing under different conditions varies in its drought resistance, the 
more hardy being that from drier habitats. Protonemata were correspond- 
ingly variable, withstanding the action of the desiccator for periods varyin 
from 2 weeks for the cultivated protonema of Funaria hygrometrica, whose 
natural grown protonema was twice as resistant, to 14 and 15 weeks for the 
natural growing protonema of Bryum argenteum and Catharinea undulata. 
The sporophytes were found to be almost as hardy as the protonemata. 
uniformity in the power of resisting cold. At —20° C. the leaves of most 
whether they came from the aquatic, mesophytic, or 
xerophytic habitats, although in a few species the resistance extended to 
—30° C. Plants grown at a high temperature showed decidedly less resist- 
ance to sudden cold than those from cooler situations. Attention is also 
directed to the relation between turgor and the ee point of the leaf cells, 
and to the behavior of the cells in various solutio 
The evidences of careful methods, the naan number of species under 
experimentation, the abundance of the quantitative data, and the logical 
organization of the report are to be commended.—Geo. D. FULLER. 
Composition and qualities of coal.—By improved methods of making thin 
coal sections, JEFFREY? claims to have obtained new and valuable results in 
the study of the composition of coal. In a brief discussion of the modes of 
accumulation he holds the view that at present both the accumulation as the 
result of heaping up of the remains of successive generations of plants in peat 
gs, the autocthonous hypothesis, and the accumulation by drift in lakes or 
lagoons, the allocthonous hypothesis, commonly take place in the temperate 
ns 
*3 JEFFREY, Epwarp C., On the composition and qualities of coal. Econ. Geol. 
9°730-742. Its. 
* 
