jsly b 





■r botanical col- 



In our first trip afield we were guided by Dr. C. G. Pringle to 

 a locality on the lava slopes of the Pedregal, a few miles south of 

 Mexico City. The irregular surface of this volcanic forma- 

 tion is pitted with cavities and caverns, some of which are large 

 enough to enclose an ordinary dwelling house, and the variety 

 of conditions of moisture and shade gives opportunity for a wide 

 range of vegetation. So luxuriantly do the plants grow in these 

 places that the openings of the caves, or pits, will be choked with 

 their branches and foliage. 



This locality has been visited by Dr. Pringle many times and 



Opum 



is a type locality for many species collected by him. We found 

 several species of prickly pear, some of which have not yet been 

 described, and it was also seen that species so closely related as 

 not to be easily separable were in the closest proximity. 



Early in September we started to examine the desert valleys 

 which lie along the main backbone of southern Mexico in the 

 states of Puebla and Oaxaca at elevations of 1,200 to 6,000 feet. 

 Tehuacan, situated in one of the northernmost of these arid val- 



