202 BOTANICAL GAZETTE [Marcy 
to make any considerable headway on the complex is due partly 
to its relative inability to extend its area by vegetative propaga 
tion, partly to its short life cycle, and partly to the impossibility 
of germination. Thus a group of cottonwoods, which germi- 
nated when the conditions were more favorable and_ have been 
able to withstand the severe environment of the dune-complex, 
cannot appreciably extend their area, nor can they live for 
: many years. New trees cannot take their place, because of the 
inability of the cottonwood seed to germinate on the higher 
exposed portions of the complex. These seeds sprout much 
more slowly than those of the bugseed, nor could the young 
plants withstand the winter conditions on the complex, evel 
should they germinate. Furthermore, the likelihood of any 
considerable lodgment of cottonwood seeds is excluded by theif 
light cottony appendages. 
“THE UNIVERSITY OF CHICAGO. 
[ To be concluded. | 
