58 



more in at least one species and nearly cover the old trunks with 

 the tightly appressed, curved and twisted cylinders completely 

 covered with spicules. If then we find these same pulvini, sub- 

 tended by leaves, upon the fruit, we can scarcely produce stronger 

 evidence of its caulome nature. 



Upon the plains east of San Luis Potosi, Mexico, there are 

 very extensive thickets of OpJintia Kleiniae, one of the tasajillos 

 of the Mexicans. The plant is exceptionally abundant in the 

 foothills and surrounding the bases of the numerous lone peaks 

 and ridges which are found upon the plains detached from the 

 main mountain range. It is associated with the maguey, mes- 

 quite, and other typically desert plants. It presents two strik- 

 ingly different aspects — indeed they are so different as to make 

 one doubt their identity, were it not for an exceptional plant in 

 which the two extremes are combined in one individual. Simply 

 a variation in the form of plants of the same botanical species 

 gives no great concern, but when as in this case the difference in 

 form is coupled with a radical difference in the fertility of the 

 fruits, the variation has an added interest. 



The form of the plant which we shall assume to be typical is 

 the most common one to be found in the general region. It is 

 that form described in the books and is an open-branching plant 

 three or four feet high. It has two forms of branches, one 

 easily separable and relatively short, while the other is longer as 

 a rule, possesses stronger and longer spines, and is firmly at- 

 tached to the parent plant. Its fruits when mature are always 

 bright red and sparingly proliferous. 



The other form, while somewhat less abundant in the general 

 region, is even more conspicuous in certain localities upon the 

 plains. It has a more congested habit of growth, a much larger 

 number of the short, easily separable reproductive branches, and 

 its fruits are often entirely green, although they are also often red 

 or with simply a blush of red, and they are exceedingly prolifer- 

 ous and produce no fertile seed. 



In both forms and in many other species of the Cactaceae the 

 fruits put forth a vegetative growth and develop into new plants 

 whenever they come in contact with the ground. These fruits, 



