2O4 J- ARTHUR HARRIS AND JOHN V. LAWRENCE. 



The purpose of this paper is to present the results of a series 

 of determinations of the concentration of the leaf tissue fluids of 

 the three genera, Avicennia, Rlnzophora and Laguncularia. 



This has been expressed in terms of molecules and ions as 

 measured by the freezing point lowering A, corrected for under- 

 cooling (Harris and Gortner, '14), and in atmospheres pressure P 

 as given in the paper just cited and in a supplementary table 

 (Harris, '16) necessitated by the high concentrations found in the 

 leaf tissues of the mangroves of the swamps on the southern 

 shore of Jamaica and in the plants of the adjacent coastal desert 

 (Shreve, '10). All determinations were based on sap extracted 

 from tissue previously frozen (Gortner and Harris, '14), to in- 

 crease its permeability, as emphasized by Dixon and Atkins 

 ('13) and ourselves ('16). On approaching the freezing point 

 or in passing it in undercooling, the sap of all three species 

 generally shows a cloudiness or precipitation as noted by Gorke 

 ('06). That this sensibly influences the freezing point lowering 

 seems rather improbable, but we have not been able to give 

 the subject adequate investigation. 



Some difficulty was experienced with slight or heavy salt in- 

 crustations which sometimes occurred on the leaves, and are not 

 easily removed without washing. To what extent this is of 

 internal origin we are not able to assert. Probably it does not 

 appreciably influence the constants upon which our discussions 

 are based. Two determinations based on leaves of Avicennia 

 from Port Henderson, Jamaica, which had particularly heavy 

 incrustations, which were probably not thoroughly removed, 

 gave : 



Mar. 30, A == 5.86, P ---- 70.0; April 2, A = 5.86, P = 70.0. 



II. HABITATS FROM WHICH COLLECTIONS WERE MADE. 



The mangroves at Port Henderson form a dense thicket in a 

 low area back of a gravelly, rather sterile beach which separates 

 the swamp proper from the open sea. The vegetation consists 

 of a dense growth of Avicennia nitida Jacq. with a few specimens 

 of Rhizophora mangle L. and Laguncularia racemosa (L.) Gaertn. f . 

 The pneumatophores of Avicennia thickly studded the water- 

 covered soil or soft mud in most of the swamp. 



