April 30^ 1915] 



SCIENCE 



657 



basis of comparison for Fitting^'s xeropliytic 

 series. Furthermore, both investigations were 

 carried out by the use of plasmolytic methods, 

 the accuracy of which when used under any 

 but the most ideal conditions is open to some 

 doubt. 



Finally, the possibility of the existence 



zona, during February, March and April, 

 1914. As a basis of comparison determina- 

 tions on species of the spring and early sum- 

 mer native and naturalized flora of the vicin- 

 ity of the Station for Experimental Evolution 

 were made.^ Each series comprised not far 

 from two hundred determinations based on a 



Draughtsman's curves smoothing the summed percentage frequencies of osmotic pressures of 

 various magnitudes in the sap of plants of the deserts around Tucson and from the various habi- 

 tats near Cold Spring Harbor, Long Island. 



within the living plant tissues of concentra- 

 tions so high as these reported by Fitting has 

 been questioned by plant physiologists. 



It has therefore seemed to us highly desir- 

 able that further series of evidence should be 

 gathered. Such data to be of real value 

 should comprise extensive series of as nearly 

 as possible comparable determinations from 

 desert and moist regions. The technique 

 which seemed to us the most trustworthy is 

 the well-known freezing-point lowering 

 method. 



The director of the department of botanical 

 research of the Carnegie Institution of Wash- 

 ington made it possible for two of us to carry 

 out a series of cryoscopic determinations on 

 the spring flora of the vicinity of Tucson, Ari- 



large number of representative species. Cacti 

 are excluded from the comparison because of 

 known peculiarities. 



The results will ultimately be published in 

 detail. Preliminarily the differences between 

 the two regions are most convincingly 

 brought out by the accompanying diagrams. 

 In these the actual frequencies of osmotic 

 pressures* of various magnitudes have been 



3 The methods used were those already described 

 (see Gortner and Harris, Tlant World, 17: 1914), 

 except for the fact that the freezing-point lower- 

 in gs were determined by vaporization of ether 

 in a Dewar vacuum tube jacket surrounding the 

 fieezing tube in which the bulb of the Beckmann 

 thermometer was inserted. 



* These are obtained directly from the depres- 

 sions of the freezing point, corrected for super- 



