$90 BOTANICAL GAZETTE [FEBRUARY 
The natural history of coal 
There is perhaps no substance of vegetable origin of greater importance 
and intellectual interest than coal. Nevertheless, we are largely ignorant of its 
i kn 
data are as open to error as the stdin of the character of a book from the 
nature of its bindings. The geologists have notably failed to give us any 
adequate description or explanation of this greatest of mineral products, and 
it is now obvious that we must look to the anatomist and the paleobotanist, 
in collaboration with the chemist and physicist, to clear up this literally as 
well as figuratively dark subject. 
R3 has stated the problem in an admirably clear and succint way, 
and has interestingly summed up the history of our knowledge of coal to the 
present time, with indications of the probable lines of successful attack in 
the future. It is noteworthy that the greatest recent modifications of our 
views in regard to coal have come about from the successful preparation of 
microscopic sections of certain types by the French investigators BERTRAND 
d RENA It is now realized that a considerable number of combustible 
minerals have been formed in open water, and are to a large degree composed 
of the remains of phytoplankton (autocthonous and allocthonous). This 
is notably the case with coals rich in gases and hydrocarbons, such as cannels, 
bogheads, oil shales, bituminous shales, etc. Our information in regard to 
the coals which are not bituminous, or at least not markedly so, is in a less 
advanced state on account of the impossibility until quite recently of securing 
sections of the coal substance sufficiently thin and decolored to show their 
organization. On this subject ARBER writes as follows: ‘If we prepare thin 
slices of coal, . . and examine them under the microscope, we shall find 
as a rule that hey are very disappointing as regards the amount of information 
we can obtain from them. Such sections are usually opaque, even when quite 
thin, and the substance is obviously very homogeneous.” Fortunately the 
difficulties here described have quite recently been almost entirely obviated, 
for it has been found possible to prepare fairly thin and translucent sections 
even by the grinding method used by the petrographer, and by a m 
biological technique it becomes feasible to prepare transparent slices of prac 
tically all categories of coals. 
e writer shows that the old chemico-physical hypothesis of the origin 
of the various categories of coal, the peat-to-anthracite theory, is no longer 
tenable, but must be replaced as our knowledge permits by biological and 
biochemical hypotheses. The nature of a coal, where we are at present 
acquainted with its real composition, depends as much as anything on the 
3 ArsEr, E. A. NEWELL, The natural history of coal. Cambridge Manuals of 
Science and Literature. pp. 163. figs. 2r. Cambridge University Press. 1911. 15: 
