October 31, 191 2 99 



under niesqiiite forest. The plants are pale and bluish beneath, 

 and the flowers very small and inconspicuous. 



Euphorbia PEDicuLiFERA Engelm. Bot. Mex. Bound. 186. 1859. 

 Tutntnanioc wash at Tucson, September 19, 1908, no. 2^08. 

 A trailing, deep rooted perennial of the sand banks. Both in 

 form and the variegated coloring of its leaves it is a handsome 

 plant, and is comparatively infrequent. As in E. setiloba^ also 

 found on the sand banks accumulated and sifted by floods, there 

 is much variation in the size and strength of flowering plants. 

 Undoubtedly this is due to the great variation in the size of the 

 grains in contiguous bodies and layers of sand, and the distribu- 

 tion of moisture and temperature therein. 



Euphorbia pycnanthema Engelm. Bot. Mex. Bound. 188. 



1859- 

 At the machine shop of the Desert Laboratory, August 31, 

 1908, no. 2^og. This plant produces dense and often large mats 

 in recently disturbed and trodden places. The leaves are elon- 

 gated, and the fruit is rounded, with a purple line on the back 

 of each capsule. In E. prostrata, the other densely matted plant 

 of waste places, the leaves are round, and the fruits sharply tri- 

 angular. The machine shop having been built this spring, the 

 species was introduced then. A somewhat aberrant form was 

 collected on Tummamoc hill, September 30, 1908, no. 2^4^^ and 

 another at the machine shop on the same date, no. 2jj2a. 



Euphorbia neo-mexicana Greene, Bull Cal. Acad. 2: 56. 1886. 

 This little annual bloomed and fruited in gravelly places of 

 the Covillea footslope near St. Mary's hospital as early as the 

 latter part of July, 1908, no. 2j/o. At first confused with E. 

 glyptosperma on account of its partly erect habit and same gen- 

 eral phase of occurrence, it was soon found to be very distinct. 

 It is a true summer annual, inhabiting the calcareous drift slope, 

 while E. glyptosperma is a perennial of the residual slope just 

 above, each remaining in its own habitat. 



