52 THE AMERICAN BOTANIST 



and Fitntunia, produce valuable rubber induced a student to 

 examine the latex of the common dog-bane (Apocynum an- 

 drosaemifolinm) with the result that the plant was shown to 

 contain a good grade of rubber. The latex coagulated with 

 acetone gave nearly one-third solids, 3% of which was rubber, 

 much better in grade than the similar product of the milkweed 

 but too small in amount to ever make our common plant a 

 profitable source of rubber. It was also found that the soil 

 has considerable influence on the amount of rubber in the latex, 

 plants from dry hills yielding much more than plants from low 

 grounds. Among other well-known members of the dog-bane 

 family are the oleander, the periwinkle, the amsonia and the 

 plant (Strychnos) from which strychnine is obtained. 



Character of Desert Vegetation. — One of the most 

 striking characteristics of the deserts of southern Arizona is 

 the diversified assemblage of vegetation forms or life forms 

 which they exhibit. These fall sharply into two classes — the 

 succulents and the schlerophylls — the former of which is rep- 

 resented by fewer species than the latter but is of quite as great 

 importance in determining the physiognomy of the vegetation. 

 Among the succulents may be distinguished the leafless stem- 

 succulent cacti, greatly diversified in size and form, the leaf- 

 succulent Agave, the leafy stem-succulent Yucca and Dasylir- 

 ion and the root-succulent Tumarnoca. Among the schlero- 

 phylls there are less striking differences of gross form, but 

 equally important distinctions in character of foliage and 

 seasonal habits. As examples may be noted Covillca with 

 small evergreen leaves, Ccltis pallida with broad evergreen 

 leaves, Prosopis and Acacia with deciduous dissected leaves, 

 Jatropha cardiophylla with broad deciduous leaves, Four- 

 qiiicria with ephemeral broad thin leaves, Parkinsonia with 

 minute deciduous leaves and chlorophyll-bearing bark and 

 Ephedra with leafless chlorophyll-bearing stems. — Plant 

 World. 



