358 The Botanical Gazette. [August, 
moisture is as marked as it is in the flat-stemmed forms. In 
October, 1893, a number of one-year-old stems of Opuntia 
In December, 1893, a number of nearly mature fruits of 
Opuntia fulgida were collected and similarly placed in an 
open box. At the end of ten months they had all developed 
long roots from the small tubercles at the base of the fruit 
but were practically nearly as green as ever. z 
The persistency with which these plants retain their moist- 
ure makes vegetal dissemination possible. With many 
species it is not necessary that the detached joints be dis- 
seminated during the rainy season. If they chance to fall to 
the ground during the driest portion of the year their con- 
tained moisture is sufficient to enable them to put forth roots 
which soon firmly anchor them to the ground, and a new 
plant is the result. 
The opuntias of Arizona belong to the two sub-genera, 
barbed and are usually more numerous and more highly de- 
veloped in Platopuntia. The spines in the two sub-genera 
differ in that in Platopuntia they are but slightly barbed, while 
in Cylindropuntia the barbed character of the spines 1s 
very pronounced. Morphologically the bristles and spines 
are the same; little is known, however, in regard to their 
functions. 
As pointed out by Dr. W. F. Ganong,! it has been tre- 
quently asserted that the function of the spines is largely 
for protection and that the readily detached and irritable 
bristles serve the same Purpose. There is no question but 
1Present problems in anatomy, . Cactacez- 
Botanicat Gazette 20: 129, 1896. morphology and biology of the 
