ECOLOGY. 339 



The transpiration rate on the south exposure is very high, with an average 

 loss of three times as much water as on the opposing slope. The sunflower 

 phytometers gave the most striking results, the plants on the south slope 

 being shorter, the stems densely pubescent, with woody bases, and the leaves 

 thicker and forming a dense terminal rosette. The plants of the north slope 

 were taller, stems less pubescent and but slightly woody, and the terminal 

 rosette larger and more open, while those at the Ruxton were intermediate. 

 The growth of the root-systems corresponded closely to the transpiration 

 rate, being greatest on the south slope, least at the brook station, and inter- 

 mediate on the north slope. 



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



In tracing the detailed movement of water in the plant, the present emphasis 

 is placed upon the concentration of the cell-sap, especially in the epidermis, 

 and the conductivity of vascular systems. A modified type of freezing-cell 

 has been devised for the former, and certain difficulties in supercooling and 

 the transfer of water before and after freezing have been solved. In the 

 epidermis of Populus tremuloides the guard-cells varied from 2.56 atmospheres 

 when closing rapidly to 23.2 atmospheres at the time of opening, while the 

 epidermal cells ranged from 6.41 to 7.20 atmospheres. A distinct gradient 

 was evident between the guard-cells and the adjacent circles of cells, strips 

 collected at 4 p. m., for example, showing the former freezing first, and, after 

 an appreciable drop in temperature, the successive rows of epidermal cells 

 freezing in turn. The melting-points of the cell-sap alone were recorded in 

 concentration readings because of supercooling, and in most of the plants 

 tried even this point was found more or less unreliable. For this reason the 

 plasmolytic method is being refined as a check or a substitute in freezing 

 determinations. 



The conductivity of the vascular system of the shoots and roots of both 

 woody and herbaceous plants is being investigated by means of a modification 

 of Farmer's apparatus. At the outset an endeavor was made to determine 

 the limits of variation for stems of the same length, position, and age, as a 

 guide in the further analysis of their behavior. In all the plants studied, the 

 successive sections of an unbranched stem show an increase in both specific 

 and absolute conduction from the base to the top. In many cases the length 

 of the stem has practically no influence, a long stem showing the same amount 

 of conduction as its parts, except when these vary greatly. Under the latter 

 condition its conductivity is determined by the section with the minimum rate, 

 a relation found to hold in Acer glabrum, Betula fontinalis, and Helianthus 

 annuus. Conduction through nodes of the sunflower is invariably greater 

 than through the adjacent internodes. On the other hand, conduction through 

 the transition region of stem and root has been found to be considerably less 

 than through the neighboring root or stem in the case of Prunus demissa and 

 other species. 



Transpiration and Stomatal Movement in Cereus giganteus and their Correlation 



with Variations in Stem Diameter, by J. V. G. Loftfield. 



The study of variations in the stem diameter of the trunk of Cereus gave a 



behavior directly opposite to that of the trees previously investigated. While 



the trunks of conifers expanded at night and contracted by day, the trunk of 



