Abstract
The observations of a number of botanists have shown that extremely high concentrations may characterize plant tissue fluids, especially when the plants 1 occur in a highly saline substratum. To Fitting 2 belongs the credit of first demonstrating that extremely high osmotic concentrations are found in some desert plants, 3 although Drabble and Lake 4 and Drabble and Drabble 5 had preceded him in showing the fundamental relationship between environmental conditions and the osmotic concentration of plant tissue fluids.
As early as 1902 Cavara reported cryoscopic determinations on saps of high concentration 6 and in 1905 gave results in full 7 for a large series of determinations made at Cagliari. His maximum values were found in the sap of halophytes growing in localities where the concentration of the soil solution progressed with the advance of the season. He reports freezing point depressions of 7.25° in Obione portulacoides, 7.48° in Salicornia fruticosa, and 7.25° to 8.50° in Halocnemum strobilaceum. His determinations were, however, made on sap extracted without the antecedent treatment necessary to render the tissues permeable as has been shown to be necessary by Dixon and Atkins 8 and others. 9 His constants are, therefore, as pointed out by Atkins, 10 probably submaximum because of incomplete extraction.
Work on the spring flora of the Arizona deserts 11 was probably carried out in a manner to obviate the objections to the preceding studies. In this series the maximum concentrations were found in Atriplex canescens, a shrub of the salt spots, in which Δ = 5.65, P = 67.5, and in Mortonia scabrella, a small shrub of the mesalike slopes, for which one determination gave Δ = 4.78, P = 57.2.
Concentrations of about fifty atmospheres have been demonstrated in the leaf tissue fluids of more or less sclerophyllous trees Capparis ferruginea and Guaiacum oficinale and in those of the succulent-leaved halophytic half shrub Batis maritima of the saline coastal flats of Jamaica. 12
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