Vol.1] Hall. — Botanical Survey of San Jacinto Mountain. 45 



than iu the other varieties, the pnbescense is sparse and straight, 

 while the general appearance is that of a mesophytie plant. It 

 will also be noticed that the spaces between the larger leaves are 

 filled in by smaller ones borne on short, arrested branches, thns 

 increasing the amonnt of leaf snrface exposed to the snn. 



In plate x is represented a specimen (the third variety 

 technically described under M. macranfha) from the borders 

 of the Colorado Desert, to the southeast of San Jacinto 

 Mountain. The plant was in reality collected at a slightly 

 higher altitude than the one figured in plate xi, but the hillside 

 on which it grew opened out directly towards the desert so that it 

 was in the Lower Sonoran Zone, where the conditions are 

 decidedly arid. The characters exhibited liy this jtlant are 

 similar to those of the one figured in i^late xii, from the 

 highest altitudes, but the xerophytic nature is somewhat more 

 pronounced. 



On examining the internal structure of these plants we find 

 variations in the histological characters running parallel with 

 those of the external characters. Examinations have been made 

 only of the leaves, cross sections of which are shown in plate 

 xiii. It is seen that in the leaves of plants from the chaparral 

 belt (fig. 1) the epidermis is composed of large cells with walls 

 about one-half as thick as the diameter of the cavity, the loose 

 tissue below the palisade layers of the mesophyll contains large 

 air spaces, and the epidermal hairs are long, straight, and two- 

 celled. In the leaves of plants from high altitudes (fig. 2) the 

 structure is very similar to that found in leaves from the desert 

 region (fig. 3), in each case the epidermal cells being small, with 

 greatly thickened outer walls, the diameter of which is about twice 

 that of the cell cavity, the air spaces being smaller and less 

 common, and the epidermal hairs shorter, often bent or appressed 

 and not infrequently only one-celled. 



We find, then, on San Jacinto Mountain three varieties of 

 Monardella macrantJia, two of which are xerophytic and one 

 mesophytie. One of the xerophytic forms comes from the 

 desert region, the other from high altitudes in the montane 

 region, while the mesophytie form occurs only at points between 

 these two regions. From this it is evident that the conditions 



