TouMEY : Fruits of some specify of Opuntia 237 



form. It is certainly changing from its original seed-bearing con- 

 dition to one of sterility. 



Plants of this species are occasionally observed bearing clust- 

 ers of short spineless branches which externally closely resemble 

 the clusters of proliferous fruits. These clusters of branches serve 

 the same purpose as the fruits in attracting animals. It is possible 

 that they have developed because of the intimate relation between 

 animal life and vegetal dissemination. The fruit is caulome in 

 structure and through its specialized use is gradually becoming ster- 

 ile. In instances where the flowers have failed to develop we find 

 these clusters of short fruit-like branches. They differ from the 

 ordinary ultimate branches only in form, size, and want of spines. 



In a number of species, specialized branches are developed which 

 are themselves disseminated, /. e., they do not aid in the dissem- 

 ination of the normal ultimate branches as in O. fulgida. In 0. 

 tetracantha^ 0. leptocaiilis^ 0. arbitscida, and other species with 

 long, slender shoots, the wand-hke branches are not fragile. They 

 are not readily detached from the plant and they are not dissemin- 

 ated through the agency of animals. Each of these species, how- 

 ever, develops many short, tumid, specialized branches (fig. 2a 

 and FIG. 3a) but little longer than the fruits. These branches 

 become readily detached, develop roots and form new plants on 

 coming into contact with the soil. Large numbers of these spec- 

 ialized branches develop during dry and adverse seasons. Under 

 more favorable conditions they are almost entirely replaced by 

 fruit. 



From the study of the fruit of many species of Opiuitia from 

 the standpoint of structure, from the similarity In external appear- 

 ance between the fruit and the ultimate ves'etative branches and 



from teratological evidence as illustrated later In this paper I have 

 been led to the following conclusions : 



1. The fruit of Opioitia is caulome in structure. 



2. Its caulome nature is probably of recent development. 



3. It has become caulome by its once superior ovary reced- 

 ing into a vegetative branch, thus making it at present inferior. 



4. The branch, which now becomes the ovary, is usually modi- 

 fied and ripens Into the structure which we term the fruit; it may 

 however become but little modified, resembling the ultimate 

 branches and continuing as a vegetative part of the plant. 



