146 CARNEGIE INSTITUTION OF WASHINGTON. 



number of pods produced on the plant (which varies from 1 to 38 or 

 more). It appears that, on the average, the more pods to a plant 

 the more beans to a pod. This relation is, however, not close; for if 

 perfect correlation be ±1.00 and no correlation be 0.00, then the 

 correlation found is represented. by +0.126 ±0.011 merely. 



RELATION OF PHYSICO-CHEMICAL PROPERTIES OF VEGETABLE SAP TO 

 ENVIRONMENTAL FACTORS. 



Dr. Harris and Mr. Lawrence, with the collaboration of the Depart- 

 ment of Botanical Research, have been engaged on a continuation of 

 work begun with Dr. Gortner upon the subject that heads this para- 

 graph. Dr. Harris reports: 



"Any attempt to influence the germ-plasm of species as a means of controlling 

 evolutionar}'- phenomena should, if it is to throw light upon the problem of the 

 methods by which evolution has taken place in nature, be made by means of 

 factors vv^hich are of fundamental biological importance in nature. Such fac- 

 tors are Hght, temperature, and moisture. Furthermore, the environmental 

 factors chosen should affect not only the soma of the individual, but should 

 have, directly or indhectly, an influence upon the developing germ-cells or 

 fertilized egg. Such work as had been published indicated that soil moisture 

 might be such a factor. It is physically or physiologically widely variable 

 from one region to another, and is of primary importance in determining the 

 characteristics of the vegetation of a region. Furthermore, evidence has been 

 accumulating that the physico-chemical properties of the cell-sap of the plant 

 individual are greatly influenced by this factor of the environment. Thus the 

 immediate environment of the developing zygote may be very materially 

 altered. 



"Our objects, then, have been to obtain a comprehensive knowledge of the 

 physico-chemical properties of saps in relation to environmental factors, as a 

 preliminary to controlled experimental studies and transplantation experi- 

 ments. 



"In the field work about 1,400 determinations have so far been made, distrib- 

 uted in round numbers as follows: 



Arizona deserts 160 



Jamaican coastal deserts 140 



Jamaican Blue Mountains, Windward rain forests, and Leeward 



slopes 480 



Long Island mesophytic, hydrophytic, and halophytic habitats. . . . 620 



"This series of determinations, which is more extensive than all others 

 hitherto published, shows, among other points, that (a) there is a relationship 

 between the growth form of the plant individual and the osmotic pressure or 

 diffusion tension of its sap; (b) that in the regions studied differences in 

 osmotic pressure of the sap of the plant species are correlated with local 

 environmental factors; and (c) that the vegetation of different regions may 

 differ greatly in the physico-chemical properties of its sap. 



"The variation from region to region in the osmotic pressure in atmospheres 

 of the extracted sap as determined by the depression of the freezing-point 

 is shown by a comparison of the Arizona deserts with the more mesophytic 

 habitats of Long Island or with the montane rain forests of Jamaica, The 

 average concentration of the juices of the spring vegetation in the region of 

 the Desert Laboratory is 19.4 atmospheres; that for the spring vegetation of 

 Long Island is 1 1 .5 atmospheres. The mean osmotic pressure of the sap of the 



