DEPARTMENT OF BOTANICAL RESEARCH. 93 



a score or more of plants that have not been seen elsewhere in the 

 United States, although some of them are common to the Sierra Madre 

 Occidental of Mexico. A few of these forms are conspicuous elements 

 in the vegetation of the Huachucas. In this range are also to be found 

 a number of species of high-mountain plants common to northern New 

 Mexico and Colorado, which do not occur in the Santa Catalinas. 



The history of the distributional movements of plants among the 

 isolated mountains of the southwest has been controlled by the mobility 

 of the plants themselves and by the physical conditions which their 

 invasions have encountered. A few cases have been discovered in the 

 Santa Catalinas which appear to represent early stages in the invasion 

 of these mountains by plants which are widespread in adjacent ones. 

 The principal evidence for this is the fact that they are now occupying 

 only an extremely small part of the terrain which is favorable to them 

 and that they show no tendency to locaUzed occurrence in the adjacent 

 mountains. Among these are Abies arizonica, Populus angustifolia, 

 Vaccinium scoparium, Cerasus crenulata, and Parthenocissus vitacea. 



During the summer of 1916 the seeds of 14 species of plants from 

 the Pinaleno and Huachuca mountains were planted at favorable alti- 

 tudes and in favorable habitats in the Santa Catalinas. No report 

 can yet be made on their fate and repeated plantings may be necessary 

 to secure conclusive results as to their abiUty to germinate, survive, 

 and spread under conditions so nearly identical with those in which they 

 occur only 60 and 80 miles away. If any of these species become 

 established it will indicate that their previous absence was due to their 

 immobiUty; however, this may have been due to different conditions. 

 Their behavior will be watched with care, as throwing Ught on the 

 manner in which natural introductions have previously taken place. 



Vital Statistics of Desert Plants, by Forrest Shreve. 



A record of the germinations, and the fate of seedHngs, of several 

 species of desert perennials was begun on an observational area near 

 the Desert Laboratory in 1910 (see Year Book for 1912, p. 58). This 

 record now extends through seven years and some of its features have 

 reached such a point that they have been described for publication. 



On the area of 557 square meters no germinations of the giant 

 cactus {Carnegiea gigantea) have been detected in eight successive 

 summers. A single seedhng found in 1910 is still surviving; it has had 

 an average growth-rate of 5 mm. per annum during the past four years 

 and has reached a height of 35 mm. These measurements, and others 

 on plants of similar size, indicate the extremely slow rate of growth 

 in seedUngs of Carnegiea. The curve of acceleration in growth with 

 increase of size was worked out several years ago and indicates that the 

 largest individuals of this cactus are from 125 to 175 years of age. 

 Vigorous half -grown plants exhibit a maximum growth of 100 mm. 



