1895.] Vegetal Dissemination in Opuntia. 359 
the spines do serve largely to protect these succulent plants 
from the ravages of animals. If they were not so protected, 
in a few years they would entirely disappear from our west- 
ern plains. Another important function, more especially in 
Cylindropuntia, is their great aid in dissemination. 
It is not sufficient that the joints grow when detached from 
the parent plant. They must find a means of transportation 
from one place to another. In cylindropuntias this is largely 
effected by means of the barbed spines which adhere closely 
to all objects which come in contact with them. 
As previously stated the spines of Platopuntia are nearly 
smooth or but slightly barbed, but with these plants barbed 
spines are not necessary to effect transportation; they are 
disseminated in an entirely different manner. 
The species of Platopuntia being mostly prostrate or semi- 
prostrate, spread out with growth, forming large oval or cir- 
cular patches. The branches creeping or bending to the 
ground take root at each joint. In the course of time, the 
Original plant dying, the several branches become independ - 
ent plants. This process is repeated until the product of a 
single plant may extend over a large area. Among speci- 
mens of Opuntia pheacantha growing a few miles east of 
Tucson I have traced nearly twenty plants to a common 
center, some of them being several rods distant. As a rule 
a dozen or more plants, in the immediate vicinity, indicate 
that they are the product of a single plant. Usually it isnot 
difficult to locate the position of the original plant long after 
€very vestige of it has disappeared. I am convinced that 
nearly all of our flat-stemmed opuntias are disseminated in 
this manner. It does not apply of course to the few upright 
forms like Opuntia chlorotica. Although these upright forms 
are not disseminated in the same way as the prostrate plants, 
vegetal dissemination is not entirely eliminated. The young 
joints of the upright species are much more easily detached 
than in the prostrate species. Cattle and other animals feed 
to some extent upon them. From one cause or another many 
of the joints are broken off. The spines, although but 
slightly barbed, are of some aid in dissemination. They raise 
the detached stems from the ground so that they are more 
easily disturbed by animals or other moving objects coming 
in contact with them and they are scattered further from the 
parent plant than they would be if devoid of spines. 
