DEPARTMENT OF BOTANICAL RESEARCH. 79 



Aside from the difficult problem of measuring and integrating the 

 effective soil-moisture conditions, it is frequently desirable, in experi- 

 mentation, to maintain these conditions constant for a longer or 

 shorter period of time, and these investigations have furnished the 

 auto-irrigator for this purpose. During the winter of 1912-13, 

 Professor Livingston and Dr. Hawkins operated a number of these 

 instruments on plant cultures in the green-houses of the Johns 

 Hopkins Laboratory of Plant Physiology, and determined the vari- 

 ations in soil-moisture content which ijiay be expected with this 

 instrument. The range of these variations proved to be exceedingly 

 narrow. These results will be embodied in a journal article. 



Mr. J. W. Shive, of Johns Hopkins University, assisted Professor 

 Livingston in Baltimore during the academic year 1912-13, carrying 

 out certain other experimentation upon the action of the auto- 

 irrigator, and also assisted in various ways at Tucson during the sum- 

 mer of 1913. The relation of the soil-moisture residue at the time of 

 wilting to the evaporating power of the air which prevails during 

 the wilting period has received further attention at the hands of Mr. 

 Shive, this work being carried on at the Desert Laboratory. This 

 line of study, begun by Dr. W. H. Brown, now of the University 

 of the Philippines (assistant in this work during the summer of 1910), 

 and continued by Professor J. S. Caldwell, now of the Alabama 

 Polj^technic Institute (assistant during the summer of 1911), has 

 proved to be of considerable importance in scientific agriculture as 

 well as in ecology and plant physiology. 



The quantitative determination of the capacity of plant foliage to 

 resist transpirational water-loss, bj^ means of the method of stand- 

 ardized cobalt-chloride paper, which was devised in 1908 by Professor 

 Livingston, in the laboratories of the Pflanzenphysiologisches Insti- 

 tut at Munich, received attention from Mr. A. L. Bakke, of the Iowa 

 State College. Mr. Bakke spent the summer of 1913 in this work, 

 as a visitor at the Desert Laboratory. His results corroborate, in 

 general, those already published by Professor Livingston and carry 

 knowledge of this matter markedly forward. The degree of water- 

 withholding capacity exhibited by leaves (their degree of xerophy- 

 tism, in the current ecological sense) can not be accurately predicted 

 from morphological examination of the leaf structures. Mr. Bakke's 

 work will appear in a journal article. 



Autonomic Movements of Stems of Opuntia, by Edith B. Shreve. 



Observational and experimental work has been continued on the 

 movements of branches of Opuntia versicolor, with a view to deter- 

 mining the exact nature and the cause of the phenomenon. Joints 

 from 1 to 5 years old on both large and small plants exhibit vertical 

 movements which vary in amount from 10° to 170° and horizontal 



