1895.] Vegetal Dissemination in Opuntia. 361 
are developed; which, although small, retain their moisture 
for a long time after being detached. Evidently the function 
of these small, easily detached joints, is for vegetal dissemin- 
ation. The fruits of two of these plants, viz. O. tessellata 
and O. arbuscula, are usually sterile. 
Opuntia arborescens, O. Whipplei, O. versicolor and similar 
species are not so well adapted for this method of dissemina- 
tion. With these plants the joints are not readily detached 
and the spines are not so strongly barbed; they depend to a 
much greater extent upon seed dissemination, as is illustrated 
in the fact that it is not an unusual thing to find seedlings of 
these plants in all stages of development. 
As a generalization it may be stated that with this great 
group of plants the adaptations for vegetal dissemination are 
inversely as their seed production. 
University of Arizona, Tucson. 
