398 BOTANICAL GAZETTE MAY 
Forests and floods.—According to Moore,‘s forests exert no controlling 
influence upon rainfall, and very little upon the flow of the water after it reaches 
the earth’s surface. While regretting the paucity of the data, he decides that the 
run-off of our rivers is not materially affected by any other factor than precipita- 
tion, that high waters are not higher and low waters are not lower than formerly, 
nor do floods occur more frequently and continue longer than formerly. In sup- 
port of his contention that forestation exerts little or no effect upon precipitation, 
he shows that the presence or absence of forest covering affects only a thin stratum 
of air over the surface of the areas in question, whereas the conditions that control 
recipitation are confined to a much greater altitude and one not affected by the 
local irregularities occurring in the lower stratum. Statistics given for the Ohio 
River basin, where deforestation has been great, show that the flow of water in that 
river has exhibited no material change for the thirty-seven years for which measure- 
ments are available-—Gero. D. FULLER. 
Evaporation and plant societies—Evaporation is regarded as a very mpor 
tant factor in determining the character of plant societies, and several ecologists, 
measuring it with the most accurate instruments now available, are collecting 
interesting data from various localities. SHaw*® determined the amount of 
evaporation at various stations in the Selkirk Mountains, ranging from 800 
to 2900 in altitude, extending his observations over a period of 12 weeks. The 
maximum evaporation was at r10o™, while above this altitude there was 4 
gradual but somewhat irregular diminution. 
Dickey,4’ in a bog habitat, found evaporation in the open central area occu- 
pied by Sphagnum, Oxycoccus, and Eriophorum much greater than in the sur- 
rounding maple-alder zone, and that rainfall had a more marked effect upon the 
rate of evaporation in the latter situation. In the maple-alder zone the appearance 
of foliage in the spring and the fall of leaves in the autumn affected the 
rate materially—Gro. D. FULLER. 
Stem gall on Commelina.—The LEEUWEN-REIJNVAANS* give a discussion of 
the gross and anatomical character of a stem gall on Commelina communts L. 
It is caused by the larva of a lepidopterous insect, Aegeria unijormis Snellen. The 
larval chamber originates in the central axis of the stem, and the enlargement of 
the stem at this point is on one side, instead of radial as is the case with most 
which originate in the central axis of the stem. The enlargement is due mainly 
to the increase in the amount of the parenchyma tissue. The collenchyma 1S 
45 Moore, WILLIs L., Influence of forests on climate and on floods. Report t 
Committee on Agriculture, U.S. House of Representatives. pp. 38. 1919. ‘ 
46 Suaw, C. H., Present problems in plant ecology. III. Vegetation and we 
tude. Amer. Nat. 43:420-431. 1909. 
47 DicKEY, Matcotm G., Evaporation in a bog habitat. Ohio Nat. 10:17-23: 
1909. F 
48 LEEUWEN-REIJNVAAN, J. UND W., Drs. von. Kleinere cecidologische Mi- 
teilungen. Ber. Deutsch. Bot. Gesell. 2'7:572-581. figs. 6. 1910. 
