Igo1 | SOUTHWESTERN CACTACEAE 55 
conditions, can best be determined by careful study. At present 
Iam inclined to believe that the most permanent and satisfactory 
evolutionary characters will be found in the fibrovascular sys- 
tem. When its metamorphosis is fully understood a far clearer 
insight can be gained, not only into the interrelationships of 
these peculiar and at present much confused groups of plants, 
but also into the steps by which they became gradually accus- 
tomed to their present rigorous habitat. 
HARVARD UNIVERSITY. 
Later investigation shows that the statement (p. 42, line 17 ff.) regarding 
periodicity of growth is incorrect. The smaller amount of growth noted was 
due to the drouth of the summer of Igoo. In spite of their storage facilities, 
these plants are apparently affected by temporary unfavorable conditions to 
a degree almost surprising. 
