300 BOTANICAL GAZETTE [ocTOBER 
concentration far higher than those of mesophytic regions, and quite 
equal to if not slightly higher than those of the winter vegetation 
of the Arizona deserts. 
While determinations based on these species growing in other 
environments are as yet too few to justify detailed discussion, it 
seems most probable that the properties of their sap are due in part 
to the local conditions and not merely to the existence here of a. 
series of species characterized by high concentration.® 
In the few cases in which constants for a species were obtained — 
from the coastal flats and from the rocky slopes, the values from 
the slopes are generally lower than those from the flats. Thus the 
single determination on Caesalpinia vesicaria from the slopes gives 
27.2 atmospheres as compared with 34.4, 34.9, and 37.0 from the 
flats. Capparis ferruginea from the slopes gives 41.9 and 43.8 
atmospheres as compared with 49.1 and 49.4 atmospheres when 
growing on the flats. Jatropha gossypifolia gives 12.3 atmospheres 
on the slopes as compared with 13.2 and 14.9 on the flats. 
In the case of Prosopis juliflora and Achyranthes halimifolia, the 
result is uncertain. The two collections of Achyranthes from the 
slope gave 29.9 and 37.9 as compared with 29.8 and 38.7 atmos- 
pheres for the flats. Prosopis on the slopes yielded sap with a 
concentration of 32.3 atmospheres as compared with two readings 
of 29.1 and 31.5 from the flats. 
To what extent the osmotic concentration of the sap of the 
sclerophyllous forms is influenced by the actual presence of salt 
in the leaves can only be determined by special methods. The 
leaves of some of the forms growing on the coastal flats, for example 
Capparis ferruginea, are perceptibly salty to the taste; others are 
not. It can hardly be doubted that the enormous variation in the 
concentration of the leaf fluids of such forms as Batis maritima and 
Sesuvium Portulacastrum, the leaves of which are practically re- 
inforced water bags, is due primarily to electrolytes absorbed from 
the soil. The fact that the various cacti are here characterized by 
sap of low concentration, as when growing in true desert environ- 
8 . * ‘3 . ve onl 
A collection of the leaves of Guaiacum offcinale from Spanish Town ga ; 
A=2.66, P=31.9 as compared with two constants each over 4° (50 a 
in the coastal flats. 
