236 TouMEY : Fruits of some species of Opuntia 



In all species the shoot is more or less condensed and fleshy. 

 The roots are also occasionally fleshy, as in O. maa'oi'hiza and 0. 

 Jilipeiidtila. More frequently the roots are of two sorts, long sur- 

 face ones for the rapid absorption of moisture, and short deeper 

 ones to give the plant support. The former are of quite different 

 structure from the latter. In many species the fruit has developed 



along special and circumscribed lines. 



Opitntiafitlgida is often a tree in habit and size, and grows best 

 in the most arid situations in southern Arizona. It seldom repro- 

 duces by natural seeding, depending almost entirely upon vegetal 

 dissemination for its reproduction. In this species the fleshy, pro- 

 liferous fruits grow in large, pendulous clusters. They are like 

 short vegetative branches, and have few or no spines (fig. i). 

 These large fruit-clusters are often sterile, and under the adverse 

 environment the seeds that do develop usually fail to grow. The 

 species, however, has become rapidly and widely spread through 

 vegetal dissemination. 



The, fruit is usually most abundant on the lower branches and 

 is within easy reach of cattle and other animals. Where undis- 

 turbed it remains on the trees for many months after maturing, 

 but because of its succulency and lack of spines it is sought after 

 by wild as well as domestic animals. In this species the ultimate 

 branches are very succulent, densely covered with spines, two 



1 



inches or less in diameter and four to eight inches long. They 

 are very fragile, becoming detached from the plant with the slight- 

 est disturbance. Animals, in their effort to get the fruit, come in 

 contact with them. The fragile branches become detached and 

 adhere to the animals like large burs,^nally to fall to the ground, 

 often after being carried for miles. The basal end of the branch 

 usually comes in contact with the soil because of the few short 

 spines at this end, roots rapidly develop, often in the driest of 

 weather, and a new plant becomes established. 



The spineless nature of the fruit, its succulency, its growing in 

 large clusters, its remaining attached to the plant for months after 

 maturity and its position within easy reach of cattle and other large 

 animals, are all important factors in vegetal dissemination. I 

 believe that the special acquired function of the fruit as an aid in 

 vegetal dissemination is gradually influencing its character and 



