CONTENTS, 



Page 



Introduction. . . ; .' i 



General aspect of the problem i 



Physiographic, climatic, and floristic features of the Sonoran desert 3 



Form-Alterations, and Growth of Cacti S 



Sahuaro (Carnegiea gigantea) 5 



Conditions and methods of measurement S 



Reversible alterations 7 



Direct adjustment to varying amount of soil- water 7 



Individual and local peculiarities 9 



Dififerences in amplitude of variation from base to apex of trunk 12 



Effects of insolation 13 



Influence of changes of air-temperature 20 



Limits of expansion.'. 23 



Variation in water-content 25 



Growth 28 



Growth in circumference 29 



Growth in height 30 



Bisnaga (Echinocactus wislizeni) 31 



Effects of insolation ~ 32 



Comparison of weights and measurements 34 



Growth 36 



Prickly pear (Opuntia sp.) 37 



Summary 42 



Variations op the Water-Balance 45 



Purpose and scope of the experiments 45 



Carnegiea gigantea 45 



Echinocactus _ 50 



Opuntia sp 67 



Micrampelis fabacea 69 



Ibervillea sonorae 70 



General Conclusions 72 



iii 



