298 BOTANICAL GAZETTE [OCTOBER 
Port Henderson region, 27.00 atmospheres; Tucson region, 22.01 
atmospheres. 
With the exception of the salt spots, the bajada slopes of the 
Tucson region show the highest concentration. Comparing with 
the rocky slopes of the coastal region, the results are: Port Hender- 
son rocky slopes, 27.00 atmospheres; Tucson region, bajada, 
30.34 atmospheres. 
Because of seasonal differences it is undesirable to attempt to 
analyze too closely the differences between the two desert areas. 
Such could be done if determinations upon the coastal deserts 
immediately subsequent to a rainy season were available. Until 
such data.are at hand and until our determinations for the summer 
flora of the Arizona deserts are ready for publication, it is premature 
to discuss the matter further than to say that both of these regions 
show concentrations far higher than do those of mesophytic habitats, 
and that they are in good general agreement between themselves. 
OsMOTIC CONCENTRATION IN THE CACcTI.—From the floristic 
standpoint the most striking feature of these coastal deserts is the 
remarkable growth of arborescent cacti in immediate proximity to 
dense mangrove swamps. From the physiological standpoint the 
most remarkable result of these studies is the demonstration that 
the fluids of these cacti have about the same concentration as those 
of other desert regions. . 
The 28 determinations made on the sap of the 7 species 
belonging to the 6 genera of cacti show a range of A=o.40 to 
A=o.93, or P=4.9 to P=11.1, with an average for the series of 
A=o.626 and P=7.52. Yet these cacti are growing in the same 
substratum as sclerophyllous arborescent species with an average 
concentration for the species of A=3.54 and P=42.4. Much of 
the cactus-covered area has a dense undergrowth of Batis maritima, 
which has an average of A=4.18, P=s0.0. Sesuvium, which 
sometimes occurs but is not so abundant as Batis among the cacti, 
has sap averaging A=2.60, P= =31.2. Better illustrations of the 
diverse reaction of two organisms to the same general environ- 
mental situation could hardly be found. These results are in close 
agreement with the findings of those who have worked on 
cacti in other regions. 
