64 REPORTS OF inve;stigations and projects. 



Physiology of Stomata. — Prof. F. E. Lloyd brought his work upon the 

 physiology of stomata to a close early in the year and presented a paper which 

 is to be published by the Carnegie Institution as No. 82 of its series of 

 publications. No important modifications of the main conclusions reported 

 concerning this work in the previous year have been made, and the principal 

 results seem to be thoroughly tested and confirmed. Professor Lloyd acted 

 as superintendent of the Desert Laboratory during the earlier part of the 

 year, in place of Mr. G. Sykes, who was detailed for special duty in the con- 

 struction of a mountain road to the Solar Observatory on Alount Wilson. 



Relative Transpiration and Variations in the Rate. — Dr. B. E. Livingston 

 has been engaged in making a general survey in which a number of plants 

 representing various physiological types have been examined with regard to 

 the performance of the transpiration function. A successful effort is being 

 made to discriminate between the physiological and the purely physical varia- 

 tions in the rates of loss of water by plants, by the use of improved methods 

 and of the conception of relative transpiration. 



The Relation of Evaporation in the Open Air to Plant Activity. — The 

 experiments of Dr. Livingston in the behavior of plants rooted in moist soil, 

 but subjected to the action of air with high and low evaporating power, have 

 established the fact that such evaporating conditions exercise a very important 

 direct influence on the plant, irrespective of its effect on soil moisture. In 

 order to survive and succeed in dry climates the plant must not only have an 

 adequate supply of soil moisture, but must have developed the power of 

 absorption and the mechanism of conduction to such extent as to supply the 

 transpiring surfaces with the necessary amount of water. A correlative 

 adaptation of course includes the various structures, such as waxy citicula, 

 which restrict transpiration. 



Evaporation and Plant Distribution. — Fragmentary evidence seeming to 

 suggest that the ratio of rainfall to evaporation is perhaps a more decisive 

 criterion for the delimitation of vegetation zones than temperature, arrange- 

 ments were made by which some comprehensive data might be obtained. 

 For this purpose Dr. Livingston distributed cup evaporimeters to 26 observers 

 in various regions in the United States, and weekly reports were returned to 

 him by the collaborators. The reduction, correction, and comparison of these 

 records is now being carried out. The prompt and active manner in which 

 this cooperative work has been carried out by the various observers has been 

 very gratifying. 



Soil Moisture. — Dr. Livingston has continued the series of analyses for the 

 purpose of determining the amount of water available for plants in desert 

 soils during dififerent seasons of the year. So far attention has been wholly 

 directed to the various types of soil included within the domain of the Desert 



