146 J. A. Harris, R. A. Gartner and J. V. Lawrence 



rain forest, and in the mesophytic habitats of the north shore 

 of Long Island, have shown that the osmotic concentration, 

 as measured by the cryoscopic method, is far higher in the leaf 

 tissue fluids of ligneous than of herbaceous species. 



A large series of determinations in the various non- 

 halophytic habitats of the north shore of Long Island shows 

 that the specific electrical conductivity of the expressed leaf 

 tissue fluids of ligneous species is lower than that of herbaceous 

 species. This shows that while the concentration of ionized 

 electrolytes is lower in ligneous than in herbaceous forms, the 

 reverse is true for total solutes. 



Because of the wide geographic range and the great 

 diversity of conditions (xerophytic, mesophytic and hygro- 

 phytic) under which the investigations on osmotic concentra 

 tion were carried out, there can be no reasonable doubt but 

 that the differentiation of ligneous and herbaceous plants with 

 respect to the magnitude of their osmotic concentration (A) 

 is a general biological law. Until confirmed by investigations 

 in other regions presenting different conditions for plant 

 growth 1 the results for conductivity cannot be asserted to be 

 of universal validity. 



The Carnegie Institution 

 of Washington 



1 These investigations are now in progress. 



