83 



acres is so intricately covered with opuntias that travel is slow 

 and difficult. At first sight, and until one has become accustomed 

 to their examination, all seem to be slightly variable forms of a 

 single species, but one presently becomes aware that the varia- 

 tions, however numerous and slight, are constant. If he is then 

 fortunate enough to secure the companionship of a competent 

 and experienced mountaineer, he will learn that all these forms, 

 and more than he has differentiated, are distinguished by names 

 and that the differences between them, such as the shade of 

 green of the surface, the form and relative thickness of the 

 joints, the shade of color of the flowers, their time of appearing 

 and the color, especially the internal color, of the fruits, and their 

 edible properties, are all well defined by the natives. I am 

 strongly of the opinion that the relation between the present 

 state of our knowledge of the Mexican opuntias, and that of the 

 future, is much like that of our knowledge of American Crataegi 







\ i 



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A ' 







'^■|F".^(i^: 



.r'-^ 



-/■ 



Fig. 3. Vitis bianco Munson. 



of ten years ago as compared with that of the present. Some 

 of these flat-jointed opuntias are old and large trees, with 

 trunks two feet or more in diameter. The huge, widely and 

 densely branching Myrtilocactiis is often conspicuous and abun- 



