. 
tg11] CURRENT LITERATURE 71 
authors apparently feel it desirable to teach as many facts as possible through 
demonstration or experiment. This probably accounts for the large number of 
experiments used for the year’s course, and for their qualitative and in many 
cases extremely elementary character. _The experiments stand quite in con- 
trast with the aims set forth by Ganonc in his manual for a college course in 
this subject. “The emphasis is thrown, for advanced or college work, not 
upon qualitative results obtained by students from apparatus of their own 
making, but upon quantitative results obtained from practically accurate or 
normal apparatus manufactured expressly for its particular use.”’ The lack 
of reliability in much of the data of plant physiology is due to the loose qualita- 
tive methods used in the subject. I know no better place to begin the develop- 
ment of reliable quantitative technique than in college and university courses. 
GANoncG has repeatedly urged this necessity. Time-honored experiments that 
have taught misconceptions ought to be dropped from manuals or modified 
so as to teach the truth. As an illustration, we may mention the use of the 
potassium bichromate and ammoniacal copper sulphate screens for the purpose 
of determining the relative photosynthetic value of red and blue light. Kyrep 
and Mrinper’ have shown that the results obtained in this case are due to 
different intensities and not to different qualities of the light. This experi- 
ment is of significance only when the screens are so arranged as to give equal 
energy values. Under this condition Knrep and MINDER found equal photo- 
synthetic activity for the two ends. When exact chemical methods give 
more trustworthy results (as is the case in experiment 35 on the retention of 
salts by soil), one can hardly see why they should be avoided in a university 
course.—WILLIAM CROCKER. 
Outlines of geologic history.—Under this title a series of essays involving 
a discussion of geologic correlation is published.6 The essays were presented 
before Section E at the Baltimore meeting (1908) of the American Association, 
and include three of interest to botanists: “‘The upper paleozoic floras, their 
succession and range,’’ by Davin WHITE; Sapeisees ie range of mesozoic 
and tertiary floras,’ by F. H. Knowiron; “Origination of self-generating 
matter and the influence of aridity upon its poae eta development,” by 
T. Macpoucat. The first two papers cited present in convenient outline 
form the succession of floras from the middle Devonian to the end of the 
Tertiary. Naturally the presentation is chiefly stratigraphic, with suggestions 
as to climatic changes; but the material for a consideration of the historical 
basis for phylogenetic conclusions is thus made more available. MacpouGat’s 
essay, as the title suggests, is highly speculative, but the basis of facts which 
5 Bor. GAZETTE 493390. IgIo. 
6 Outlines of geologic history with especial reference to North America. Sym- 
posium organized by BarLey Witus. Compilation edited by Roti D. SatisBury. 
Chicago: The University of Chicago Press. 1910. $1.50. 
