1917] HARRIS & LAWRENCE—TISSUE FLUIDS _ 303 
Hitherto unpublished determinations made in the summer of 
1916 by LEamon and Harris give: 
Santa Catalina bajada 
Edge of arroyo, July 6, A=2.63, P=31.6 
Same tree, August 14, A=2.40, P=28.8 
Upper bajada, July 6, A=2.87, P=34.5 
Mesa-like slopes, July 24, A=2.51, P*30.1 
Surely no one will venture to assert on the basis of the available 
data that the Jamaican Prosopis juliflora and the southwestern 
P. velutina are sensibly different in osmotic concentration. 
With regard to the cacti, which have been shown elsewhere in 
this paper to have about the same concentration of tissue fluids as 
those found for this group growing in other habitats, the following 
points must be taken into account. The cacti are plants char- 
acterized by a deeply penetrating anchoring root system and a far- 
reaching superficially placed absorbing system. The evidences 
upon which this statement is based are chiefly those presented by 
Cannon in his large paper on the root habits of desert plants. If 
the coastal species agree in this regard with the forms which have 
been investigated, their absorbing organs are in contact with the 
actually dryest zone of the substratum during periods of severe 
drought, and with one physiologically dry, that is, characterized by 
a soil solution of high osmotic concentration, during periods of 
moderately abundant soil moisture. 
Such are the conditions which result in the high concentration 
found in Batis maritima, and one might, at first thought, suppose 
that the cacti would also be subject to the same conditions. Two 
additional factors, however, are to be taken into account: (1) the 
cacti are organisms capable of rapid storage of water during tran- 
sient periods of soil saturation, and its persistent retention during 
* The point is splendidly illustrated by two photographs of Opuntia published by 
CANNon (Amer. Nat. 40: cies fet: 2~3. 1906). MacDovcat and Spatpine (The 
water balance of succulent p Publ. Carnegie Inst. Wash. 141. 1910) have 
dealt with the problem in Sas aeart A number of other papers bearing more or 
less directly upon the general pro blem of water absorption and storage in the cacti 
have since appeared from the Desert Laboratory 
