fl>ostelsia 29 



The plants growing at the sides of 

 the lower mountain roads are generally 

 the same species as are found on the 

 plains. As higher altitudes are reached, 

 however, the number of characteristic 

 roadside weeds diminishes. The follow- 

 ing plants generally thin out or com- 

 pletely disappear at the altitude named: 

 Euphorbia marginata 2300 meters, 

 Cleome and prickly lettuce 2400 meters, 

 Mexican poppy 2500 meters, Grindelia 

 and Iva 2600 meters, plantain and 

 shepherd's purse 2700 meters. The 

 figures just given are correct only in 

 a very general way, since the distri- 

 bution of these plants is determined 

 not only by climatic and edaphic con- 

 ditions, but also by opportunities for 

 the dissemination of seeds. In the 

 town of Ward, one of the oldest min- 

 ing camps in the State, where there 

 has been a good opportunity for dis- 



