1918] CURRENT LITERATURE 197 
Cleistogamy in Heteranthera.—WYLIr” has discovered that Heteranthera 
dubia is cleistogamous, and his investigation of the situation has led him to 
some interesting conclusions and questions. As he remarks, this plant “has 
specialization adequate to insure cross-pollination.” e s that there is 
no possibility of cross-pollination, except through flower elongation, “‘so that 
if seeds are to be set with certainty and in considerable numbers, it must be 
through close pollination under water, excepting the relatively few flowers so 
situated that they can reach the air, and these also seem to have acquired the 
habit of self-fertilization.”” He suggests that this species is a favorable one 
for experimental study in plant-breeding, since it grows readily, and if kept 
submerged sets seeds freely without further attention —J. M. C. 
A living physical system.—Briccs’s* clear-cut picture of the living plant 
as a physical system which is absorbing energy and performing useful work is 
significant of the present trend of botanical thought. He suggests that the 
doctrine of vitalism is being restricted more and more as our knowledge of 
plant phenomena increases. He summarizes the situation as follows: “The 
chemical school as ‘unknown.’” He treats the subject under the following 
heads: (1) the efficiency of the plant system, (2) the growth rate, (3) gas 
exchange between the leaf and the air, (4) diffusion through perforate septa, 
(5) the ascent of sap. In closing he emphasizes the fact that as a means of 
efficiency in plant production it is important to have the fullest possible under- 
standing of the physical and chemical processes associated with growth.— 
Geo. B. Rice. 
Leaf duration in evergreens.—In studies embracing 9 gymnosperms and 
22 angiosperms, growing in the state of Washington, Pease“ has investigated 
the duration of leaves and has endeavored to account for the variations dis- 
played. The leaf age limit reaches from about a single year in Rhamnus 
Purshiana to 23 years in Taxus brevifolia. From determinations upon approxi- 
mately roo twigs of each species grown under a variety of conditions, graphs 
are plotted showing the range for each. Some of the factors found to be 
efficient in affecting duration are (1) age, mature trees having older leaves; 
” Wyte, Rosert B., Cleistogamy in Heteranthera dubia, Bull. Lab. Nat. Hist. 
State Univ. Iowa 7: 48-58. 1917. 
*s Briccs, Lyman J., The living plant as a physical system. Jour. Wash. Acad. 
Sci. 7:89-111. 1917 
“4 PEASE, vinta A., Duration of leaves in evergreens. Amer. Jour. Bot. 4:145- 
160. figs. 12. 1917. 
