1915] CURRENT LITERATURE 69 
and maize (known locally as mealie), and vast areas have been extensively 
modified by grazing and burning. In the modified veld Aristida junciformis 
largely replaces Anthistiria. The bush, vlei, and other types of associations 
‘are much less extensive about Pietermaritzburg than are those of the veld. 
The paper is accompanied by a map, indicating the areas ocenpied by the 
different associations—H. C. Cow es. 
e origin of coal.—A recent bulletin?’ from the Bureau of Mines presents 
the results of extensive researches as to the origin of coal, long a vexed question. 
WHITE discusses the geologic relations of coals, analyses of coal samples studied 
under the microscope, physiographic conditions attending the formation of 
coal, rate of deposition of coal, and regional metamorphism of coal. Davis 
contributes an account of the origin and formation of peat; while THIESSEN 
escribes in detail the results of a microscopic study of coal, prefacing his 
account with a full historical review of the subject. The bulletin is so full of 
important facts and interesting inferences that it is impossible to recount 
them here, but some of the general conclusions may be mentioned. 
An important conclusion is that all coal was laid down in beds analogous to 
the peat beds of today; and that all kinds of plants, in whole or in part, went 
into the deposit. The various materials entering into the structure of plants 
differ widely in their resistance to the various agencies that were concerned 
the most resistant in the residue called peat. The various processes referred 
to above, conducted chiefly by biochemical agencies, are taken up and con- 
tinued by “dynamochemical” agencies, through various later stages, resulting 
in the different grades of coal, as lignite, subbituminous, bituminous, canne 
coal, and anthracite. “Coal, therefore, is chiefly composed of residue con- 
sisting of the most resistant components, of which resins, resin waxes, waxes, 
and higher fats, or the derivatives of the compounds composing these, are the 
most important.” These substances perform mainly protective functions in 
plants, as in cuticles, spore exines (including pollen), bark, cork, and waxy © 
coverings. A very interesting result of these investigations is that any algal 
origin of coal was not demonstrated, — this has been a conspicuous 
and perhaps favorite theory—J. M. 
Water requirement of plants.—The ratio of the amount of water taken 
up by a plant during its growth to the dry matter produced has been found 
to vary very much, and it would seem that its careful investigation would 
* Warre, Davin, and Tuiessen, REINHARDT, The origin of coal. Bull. 38, Dept. 
Interior, Bureau of Mines. pp. se pls. 54. 1913- 
