No. 1, May, 1921] ECOLOGY, PLANT GEOGRAPHY 13 



ally only about one-third occurs during the season of growth. Sometimes the water content 

 of the soil to a depth or 3 or 4 feet is reduced to the point where it is not available for plant 

 growth. Roots penetrate more deeply in loess than in glacial drift soils. Aeration may also 

 be a factor of importance in these differences in root penetration. — The chaparral community, 

 between the Ohio-Missouri forest complex and the prairies to the westward, have plants with 

 well developed absorbing systems. The roots penetrate to a depth of 5.5 to 21 feet, but all are 

 deeply placed. Vegetative propagation is a feature in this community. — In the plains the 

 plants are more deeply rooted than in the prairies although the extreme depth attained in 

 certain instances was found to be less. The generalized type of root system is most common. 

 The precipitation is about 15 inches, 80 per cent of which falls during the season of growth. 

 Water does not penetrate to a depth greater than 13 feet, or that marking the deepest placing 

 of the roots. The prominence of shallow, widely spreading laterals is a feature of certain 

 species, as in the cacti and in Yucca. At certain periods during the summer no water is avail- 

 able in the soil for plants to a depth of 5 feet, and it is uniformly dry to a depth of 7 feet. 

 The subaerial plains environment is characterized by active wind movements, great daily 

 fluctuations in air temperature, and relatively high evaporation throughout the growing 

 season. — In the sandhills the roots are various, although long, widely spreading roots in the 

 upper soil stratum, within 2 feet of the surface, are possessed by nearly all of the species 

 studied. Several plants which develop deep roots in the plains have only shallow roots in 

 the sandhills. The subaerial environmental conditions are similar to those of the plains and 

 differences in root development are attributable to edaphic causes. The upper 2-3 feet of 

 soil carry more moisture than the deeper soil. The most extensive root system of any seen, 

 that of Ipomoea leptophylla, was found in this community. — In the gravel-slide community 

 the roots of all plants are shallowly placed, few lying below a depth 1.5-2 feet. This is related 

 to the frequent summer showers of little penetration. The roots in the half-gravel-slide are 

 shallowly placed, as in the gravel-slide, but also supplementary deep roots are developed. 

 This is related to more favorable deep-soil conditions. Intense shallow-root competition 

 occurs in the half-gravel-slide. Reliance on water of the deeper soils, a feature of this com- 

 munity, carries the plants over periods of drought. — In the forest a relatively shallow-rooted 

 condition is to be found and this is true of many trees as well as of lesser plants. This char- 

 acteristic is related to the distribution of moisture in the soil, which is most abundant in the 

 surface layers. The roots also have relatively poor lateral development. — Where species 

 occur in distinctly different habitats the root development generally conforms to the com- 

 munity root type, although exceptions were found in a few instances. — W. A. Cannon. 



98. Weaver, J. E. Ecological relations of roots. [Abstract.] Publ. Nebraska Acad. Sci. 

 10: 15-16. 1920.— See Bot. Absts. 8, Entry 97. 



VEGETATION 



99. Andersen, Emma N., and Eld a R. Walker. An ecological study of the algae of 

 some sandhill lakes. Trans. Amer. Microsc. Soc. 39:51-84. PI. 3-12, jig. 1-17. 1920.— 

 This study was made in Cherry county, western Nebraska, in the sandhill country abounding 

 in bodies of water. The latter vary in size from mere ponds to lakes 3 or 4 square miles in 

 area, and in depth from 2 to 15 feet. The lakes are surrounded by grassy meadows and sand 

 dunes. The climate is dry, windy, hot in summer and cold in winter. By analysis the water 

 of the different lakes varies in alkalinity from 111 to 1129 parts per million. Many migra- 

 tory birds visit the lakes, probably bringing the spores of many algae on their feet. — The 

 work was limited to a few localities representative of the different types of habitat of the 

 region. Climatic conditions — daily variations of temperature of air and water at different 

 depths — were obtained by use of standard instruments. For the study of light intensity at 

 different depths a modification of the solio photometer was used. — 'The lakes were found of 

 fairly uniform temperature, aeration, and alkalinity. Two factors influence the distribution 

 of algae, light and mechanical support. Nine lakes were studied, and lists of algae found in 

 early summer, midsummer, and in October are given. It Is concluded that the occurrence of 

 algae in a given body of water is due largely to seasonal periodicity, mineral and gas content 

 of the water, and light intensity. — S. H. Essary. 



