DEPARTMENT OF BOTANICAL RESEARCH. 97 



such apparatus the shoots are exposed to the temperature of the air, 

 or, if desirable, the entire apparatus can be placed in a glass cage whose 

 temperature can also be controlled independently of the root thermo- 

 stat. In order to expose the cultures to different temperatures, the 

 glass tubes are changed from one thermostat of a certain temperature 

 to another of a different temperature. 



By the use of the root thermostats described, the effects on root- 

 growth of factors other than temperature, or in addition to tempera- 

 ture, can also be observed. For example, the effect of various gases and 

 of variation in aeration of the soil, as well as the effect of different kinds 

 of soil and differences in soil-moisture, can be studied and measured. 

 The method, in short, is found suitable for the study of the activities 

 of roots in a great variety of ways, and in a manner which places the 

 plants observed under relatively small departures from the normal. 



Temperature, Transpiration, and Water-Content of Leaves, 

 by Edith B. Shreve. 



Since August 1913, an investigation of the water relations of some 

 of the typical desert plants has been carried on, with a view to deter- 

 mining the behavior of (1) the same species at different seasons and 

 of (2) different species of annuals at the seasons in which they grow. 

 The plants now under investigation are as follows: two perennials, 

 Parkinsonia microphylla and Encelia farinosa; a winter annual. Strep- 

 tanthus arizonica; a summer annual, Amaranthus palmeri; and also a 

 plant which can be grown in the green-house at any sesiSon,Phaseolus 

 sp. At intervals of 2 to 4 hours measurements have been made of 

 transpiration, leaf and stem water-content, leaf temperature, and 

 stomatal openings. Samples of leaves have been preserved for ana- 

 tomical study, and records of air temperature, humidity, evaporation 

 from the porous-cup atmometer, and of soil water-content have been 

 kept during the experiments. 



Thus far the data have not been worked over sufficiently to warrant 

 the statement of any conclusions, but a few facts have appeared, as 

 follows: (1) The variability of the water-content of the foliage from 

 different branches and from different plants, taken at the same time, 

 must be found experimentally before conclusions can be drawn regard- 

 ing the hourly variation of leaf water-content of any species; (2) no 

 adequate comparison of leaf water-content, transpiration, stomatal 

 openings, or leaf temperature can be made unless all the plants used 

 have had the same history in regard to approximate age, soil water- 

 content, and general atmospheric conditions; (3) a variation in the 

 water relations takes place with the seasons; (4) incipient drying has 

 appeared in the xerophytic forms, under conditions of high evapora- 

 tion; (5) leaf temperature goes above air temperature, in sunlight, in 

 the case of leaves of the xerophytic type, and remains below air tern- 



