ECOLOGY. 291 



and A. glabrum proved to be nearly twice as great as that of the con- 

 ifers. The results indicate that the conifers studied are more xero- 

 phytic than the broad-leaved species during the summer and that the 

 needle habit is practically as efficient as the deciduous one in prevent- 

 ing serious water-loss in the winter time. 



Ldght Measurements, by F. E. Clements. 



The study of Hght intensity and quaUty has been continued during 

 the summer at various points in the West, and especially at the Alpine 

 Laboratory. Repeated measurements from 1902 to 1912 indicated 

 that the light intensity on high peaks, such as Pike's Peak and Mount 

 Garfield, was scarcely or not at all higher than at points 6,000 to 8,000 

 feet below. In spite of the fact that this does not conform to the 

 theory, it seems to be readily explained by the low humidity and the 

 absence of dust and other impurities. In order to test the effect of 

 high humidity, readings have been made at several points along the 

 Pacific Coast for comparison. Further tests of the quaUty of forest 

 hght have been made with a new portable spectro-photometer. All of 

 these have confirmed earlier observations to the effect that forest 

 Hght is ''white hght" and contains the various rays in essentially 

 their normal proportion. Unfortunately, no opportunity has yet been 

 found for testing the Hght quahty in such dense forests as those of 

 cedar and hemlock on the Pacific Coast and of beech in the East. 



Ecology of Root Systems, hy J. E. Weaver. 



The root sytems of a large number of dominant and subdominant 

 species of important plant communities have been examined with 

 reference to their relation to the nature of the soil, the amount and 

 penetration of the water-content, and to competition with each other. 

 Studies have been made in the climax prairie at Lincoln and the sub- 

 climax prairie at Peru, Nebraska, the short-grass plains and sandhills 

 at Colorado Springs, and in the gravel shde, half-gravel shde, Douglas- 

 fir, and Engelmann-spruce forest at the Alpine Laboratory. In all, 

 134 species have been studied, the great majority of which are perennial 

 herbs and grasses. These are distributed among the various commun- 

 ities as follows: prairie, 41 species; plains, 30; sandhills, 14; gravel 

 shde, 9; half -gravel shde, 12; forest, 17. In addition, a special study 

 was made of the roots of 12 polydemic species which exhibited ecads 

 in several different habitats. The method employed was to excavate 

 a trench to permit a complete \dew of the root system in its entire depth 

 and breadth. This sometimes required trenches 25 feet deep and 15 

 feet long. In the case of Yucca glauca, roots were traced in all direc- 

 tions to a distance of over 30 feet from the parent plant. All root 

 systems were dra-VMi to scale or photographed in position whenever 

 this was possible. 



