BOTANICAL RESEARCH — MACDOUGAL. 1 23 



course of such experiments before definite results may be expected ; but with 

 this species the progress of four years is already available, and it may be 

 expected to furnish data of importance within a short time. 



The Movements and Distribution of Desert Vegetation, by Prof. V. M. 

 Spalding. — During the past year a comprehensive ecological study of the 

 plant associations and their habitats on the reservation of the Desert Botan- 

 ical Laboratory and adjacent territory has been undertaken. This study has 

 been greatly facilitated by a topographical surv^ey, which has been completed, 

 and a geological survey, now in progress, under the direction of the geological 

 department of the University of Arizona. It is based, primarily, upon deter- 

 minations of habital factors by several members of the staff of the Desert 

 Laboratory, and upon definite observations and records of the occurrence, 

 habits, structure, and physiological activities of characteristic plants of this 

 district. Twelve well-defined habitats, each with its own association of 

 plants, have been studied, and, at the several stations located for this purpose, 

 some progress has been made in an attempt to correlate plant behavior with 

 known factors of environment, particularly as regards relation to water sup- 

 ply, alkalinity of soil, exposure, and drainage. Curves have been constructed 

 showing relative frequency of some of the m.ost characteristic species of 

 typical localities. Areas of uniform size have been permanently located, and 

 their vegetation charted and photographed. The invasion of a number of 

 species has been watched and their present position indicated on charts. By 

 these and other means data are accumulating for a rational study of compe- 

 tition, succession, and adaptation as they are exhibited in this region. An 

 analysis of the flora has been made and certain relations to floras of other 

 regions established, thus preparing for a more comprehensive study of histor- 

 ical factors than has hitherto been made in this territory. Up to this time 

 only limited districts in southern Arizona and New ^Mexico have been worked 

 over critically, but preparations are being made for the necessan,' extension 

 of the area in which comparative observations are carried on. 



Seasonal and Other Variations in Volume of Succulents, by Mrs. B. S. 

 Spalding. — Measurements of the bodies of several succulents in which the 

 water-storage function is well developed have been continued from last year, 

 and a great amount of well-authenticated data showing rapid and relative 

 great alterations has been obtained. Evidence has been accumulated that 

 the changes in the shape and volume of the saguaro (Cereus giganteus) are 

 controlled not only by its water content but in a minor degree by temperature 

 and illumination. It is hoped to continue these measuremicnts and determine 

 the parts played by the separate factors, and at the same tim.e differentiate 

 the changes in question from growth accretions. JNIeasurements have also 

 been taken of a number of individuals of bisnaga (Echinocactus) and of 

 Opuntia engelmannii. 



