1917] CURRENT LITERATURE 347 
reaction with CaCO; of the substratum, thus forming Na,zCO;. Extensive 
studies of this sort can add much to our knowledge of the absorption of salts 
by plants and intereffects of salts upon each other as regards absorption.— 
Wm. CROCKE 
Calcium compounds of the soil.—Under this titles E. C. Saorrey, W. H. 
Fry, and W. Hazen, members of the Bureau of Soils, have analyzed 63 soil 
samples of 23 types from 24 locations of 19 states. They have calculated the 
percentage of calcium combined with humus compound, calcium carbonate, 
calcium sulphate, and calcium as difficultly and easily decomposed silicates. 
They find a wide variation in total calcium content and in calcium carbonate 
and the two classes of silicates, and there was no constant relation between the 
total calcium content and the percentage of any of the calcium compounds. 
Calcium combined with humus compounds was absent in 29 soils. type 
which is recognized as a good alfalfa soil is characterized by high calcium 
content, but low content of calcium carbonate. This indicates, as does other 
evidence, that alfalfa requires a rather high content of calcium ion as a nutrient 
or balancer of the soil solution, rather than merely calcium carbonate as a 
neutralizer of acidity —-WM. CROCKER. 
Phylogeny of ferns. —Bower,® in continuation of his phylogenetic studies 
of the ferns, has developed some obs iie conclusions in reference to what 
he calls the “‘acrostichoid condition,” meaning the spreading of exposed 
sporangia “uniformly over a considerable area of the sporophyll.” This fact 
was the basis of the old genus Acrostichum, which Bower has come to regard 
not as a natural genus, but as a state or condition which may have been attained 
along a number of phyletic lines. In the present paper he has presented a 
number of genera which he regards as “‘dipterid derivatives,” that is, derived 
from a phyletic stock characterized by Dipteris, which show various stages of 
advance toward the acrostichoid condition. According to this view, a number 
of so-called genera of ferns are form genera, not being what Bower calls 
“phyletic unities.”” The increasing evidence of parallelism in evolution is 
raising the question of ~ Phyletic unity” in connection with all of our larger 
genera.—J. M. C. 
Pine forests of Virginia and the Carolinas.—Harper®” recently devised a 
method for securing a rough quantitative analysis of vegetation from notes 
taken at frequent intervals from the car window or while walking through the 
country. He made such notes during 53 hours of railroad travel and 21 hours 
35 Jour. Agric. Research 8:57-77. 1917. 
Bo ., Studies in the phylogeny of the Filicales. VI. Ferns showing 
the ““acrostichoid ” condition, with special reference to dipterid derivatives. Ann. 
Botany 31:1-39. pls. 1, 2. figs. 15. = 
37 Harper, R. M., and vegetation of northern Florida. Ann. Rep. 
Fla. Geol. Survey 6:163-437. ro 
