ECOLOGY. 391 



Slope-Exposure Studies, hy F. E. Clements, Dolly Lutjeharms, and T. J. 



Fitzpatrick. 



The opposed slopes of Engelmann Canyon at the Alpine Laboratory- 

 are being investigated with reference to the factor differences of 

 north and south exposures, and the correlation of function, growth, 

 and vegetation with the effective factors. Two opposite stations at 

 the same level have been selected, one in the gravel-slide community of 

 Aletes on the north exposure, and the other in the pine woodland on the 

 south exposure. A third station is located on the banks of Ruxton 

 Creek in the bottom of the canyon. Humidity, temperature, wind, and 

 evaporation are measured by means of recording instruments in each 

 habitat, and light and water-content by weekly readings. 



A battery of phytometers has been installed in each station. The 

 plants employed are HeUanthus annuus, Smilacina stellata, and 

 Prunus demissa. The sunflowers were started from germinating 

 seeds, while Smilacina and Prunus were transplanted into containers 

 from their natural habitat. The rate of growth and transpiration 

 was measured weekly in all three, and the wet and dry weight were 

 determined for sunflower. Sunflowers were also placed in larger 

 containers to serve as a check on those in the smaller ones. Finally, 

 seedlings of Populus tremuloides were planted in sealed garbage-cans 

 to permit measurements of the transpiration of trees on the different 

 exposures. 



The factor results so far obtained indicate that the two slopes are 

 closer in air than in soil conditions, the water-content, for example, 

 being greatest at the Ruxton, much less on the north exposure, and 

 least on the south one. The sunflower phytometers yielded the 

 greatest stem height and diameter at the Ruxton, but the lowest 

 transpiration, while size was next on the south exposure and trans- 

 piration greatest, and these were more or less intermediate on the 

 north exposure. 



The Water Cycle in Plants, hy F. E. Clements and J. V. G. Loftfield. 



A comprehensive investigation has been begun of the water rela- 

 tions of plants, with especial reference to their complete behavior. 

 Recent studies have emphasized the fact that stomatal changes and 

 transpiration can be understood only when the sap-content of the 

 leaf and plant as well as the water-content of the soil are known. The 

 rate of conduction through the fibrovascular system is likev»'ise re- 

 quired, as this determines the relation between sap-content and water- 

 content. Furthermore, the existing divergence of opinion as to the 

 echard for different species demands an extensive reinvestigation of 

 this problem under field conditions. The role of soil-air and of acidity 

 needs to be taken into account much more fully than heretofore, and 

 finally, it has become evident that a study of water relations can not 



