240 The Plant World. 



the first two pentads is undoubtedly due to severe erosion having 

 destroyed many of the individuals from 50 to 60 years of age. 

 The steepness of the slope, the instability of the soil and rock 

 covering, together with the shallow rooting habit of the Giant 

 Cactus make it certain that the curve of establishment, as con- 

 trasted with this curve of the age of the survivors, would fall 

 much more rapidly, and it is altogether likely that it would not 

 rise during the first two pentads, but would fall from a high rate 

 of establishment between 40 and 50 individuals per pentad. 



The striking fall in the establishment rate of the Giant 

 Cactus shown by these two curves compels the conclusion that 

 it is not maintaining itself in either of two situations, one of which 

 offers the highest average water-content of any desert soil away 

 from stream beds, and the other the temperature and other 

 conditions which have brought about in it the densest Giant 

 Cactus population that can be found in any habitat. It is 

 bootless at this time to attempt to explain the apparent decadence 

 of the Giant Cactus. A fuller knowledge of its germination 

 and the behavior of its seedlings, together with a more complete 

 knowledge of the periodicity of certain climatic elements within 

 its range will be sure to throw light on the fall in its rate of es- 

 tablishment. 

 The Desert Laboratory, 



Tucson. 



\ MISTLETOE IN THE SOUTHWEST. 



I, By J. C. Blumer. 



So far as collected by the writer, the Loranthaceae, para- 

 sitic upon trees and shrubs, their distribution naturally limited 

 by that of their hosts, are represented in the Southwest by ten 

 species and varieties, belonging to two genera, Phoradendron 

 and Razoumofskya. The latter comprises two species, both of 

 which belong to the mountains, and have the pines for their 

 hosts. Both species, Razoumofskya robusta and R. divari- 

 cata (?),have been collected in the Rincon and the Chiricahua 

 mountains, the latter upon Pinus chihuahuana, thickly infesting 

 some trees, the former upon P. arizonica and P. mayriana. 

 Apparently the same species, not fully developed in two cases, 



I 



