30 



SCIENCE 



[N. S. Vol. XLVI. No. 1176 



borne by the trees. If one turns to the 

 literature in search of work of a quantita- 

 tive nature on the physiology of this taxo- 

 nomically and morphologically diversified 

 group of plants, his search will be prac- 

 tically in vain. Material progress has al- 

 ready been made in the study of the sap 

 properties of some of the representative 

 types, although it is quite too early to dis- 

 cuss in detail even this phase of the physi- 

 ology of these plants. 



Osmotic concentration in these forms is 

 generally exceedingly low, Orchidacefe 

 from the Jamaican rain forest show an 

 average of 3.34 atmospheres, those from the 

 Florida hammocks an average of 4.88 

 atmospheres. Tank epiphytes from the 

 Blue Mountains of Jamaica show concen- 

 trations ranging from 2.8 to 5.5 atmo- 

 spheres. Comparable values are found in 

 subtropical Florida. 



The succulent Peperomias and some 

 other epiphytic species are also character- 

 ized by a concentration of their tissue fluids 

 only a fraction of that obtaining in the 

 foliage of the arborescent plants of the 

 same forests. 



Thus, in general, epiphytic species are 

 characterized by low osmotic concentra- 

 tion., This is not, however, a necessary con- 

 dition of epiphytism. Determinations are 

 available for at least one species of epi- 

 phytic fern showing a sap concentration 

 roughly three times as high as that gen- 

 erally characteristic of the succulent 

 Orchidacece and Piperacese and the tank 

 BromeliaccEe. 



The keen botanical interest aroused by 

 parasitic flowering plants has found ex- 

 pression in an enormous number of macro- 

 scopic and microscopic morphological and 

 life-history investigations. Yet it should 

 be clear that the problem of the distribu- 

 tion of parasitic forms, both among the 

 possible host plants of a particular region 



and from region to region, is primarily a 

 physiological one. Among the possible 

 factors, the relative concentration of the 

 tissue fluids of the photosynthetie and 

 transpiring organs of the host and para- 

 site seems on a priori grounds one of the 

 greatest importance. Studies on the 

 osmotic concentration of the tissue fluids of 

 Jamaican LoranthaCeaj on various hosts 

 have shown that in general but not invari- 

 ably, the osmotic concentration of the 

 fluids of the leaves, or of the leaf homologs, 

 of the parasite is higher than that of those 

 of the host. 



In the foregoing discussion only a por- 

 tion of the results of studies already made, 

 but as yet largely unpublished, have been 

 lightly touched upon. They are illustra- 

 tive merely. For the mass of facts justi- 

 fying generalization, the published tables 

 must be consulted. Enough has, perhaps, 

 been said to indicate the fundamental sig- 

 nificance for the physiological phases of 

 phytogeography of the physico-chemical 

 measurements. As phytogeography be- 

 comes more and more a problem of the 

 physiology of individual species of plants, 

 investigated in their own environment, as 

 methods become more precise, and as re- 

 sults are recorded and discussed in more 

 quantitative terms, the ecologist's sector of 

 the attack upon the great problem of the 

 relationship of the organism to its environ- 

 ment will be increasingly successful. Con- 

 currently, the relations of chemistry to 

 botany will become more clearly defined in 

 a field in which its existence has hereto- 

 fore been little recognized, and the service 

 of chemistry to botany will be increasingly 

 great. J. Arthur Harris 



SCIENTIFIC EVENTS 



MEMORIAL TO SIR WILLIAM RAMSAY 



The following appeal has been issued by a 

 committee formed to raise a memorial to the 

 late Sir William Ramsay. 



