DEPARTMENT OF BOTANICAL RESEARCH. 79 



Osmotic Concentration of the Tissue Fluids of Desert Plants, by J. Arthur Harris. 



The studies on the relationship between the physico-chemical proper- 

 ties of the sap of desert plants and their local distribution, carried 

 out in the vicinity of the Desert Laboratory and briefly mentioned 

 in a preceding report (Carnegie Inst. Wash. Year Book for 1915, 

 p. 81), have recently been published (Physiological Researches, vol. 11, 

 pp. 1-50, 1916). These studies were made in the period of winter 

 vegetative activity in 1914. During the summer of 1916 Dr. Harris, 

 assisted by Mr. William G. Learaon, devoted the months of July and 

 August to the investigation of the sap properties of the annuals and 

 perennials active during the summer. A series of about 300 deter- 

 minations of osmotic concentration was made, based upon collections 

 from habitats ranging from Mount Lemmon, in the Santa Catalina 

 Mountains, phytogeographically studied by Shreve (Carnegie Inst. 

 Wash. Pub. No. 217), to the Desert Laboratory domain and immediate 

 vicinity, where a large part of the field physiological investigations 

 published from this Laboratory have been carried out. In view of the 

 differences already demonstrated in the osmotic concentration of the 

 sap of plant species of different habitats, a comparison of the vegeta- 

 tions from selected points in such a gradient as that from the driest 

 mesa and the most highly developed salt spots of the desert floor to the 

 densely forested slopes of the higher Santa Catalinas has many obvious 

 points of interest, both physiological and phytogeographic. 



For comparison with these studies on the southwestern deserts, a 

 series of determinations have been made from other similar as well 

 as highly dissimilar enviromnents. Papers on the coastal deserts of 

 Jamaica and on the rain forests of the Blue Mountains of Jamaica, 

 concerning which a pubhcation has already appeared,^ will be ready 

 shortly. Extensive observations on the vegetation of subtropical 

 Florida and on the mesophytic environments of the Station for Experi- 

 mental Evolution, in collaboration with which three studies are being 

 made, are also under way. 



Osmotic Properties of Tissue Fluids of Parasitic Plants, by J. Arthur Harris. 



In an early pubhcation from the Laboratory appearing in the 

 Institution series (MacDougal and Cannon, Carnegie Inst. Wash. Pub. 

 129) the suggestion was made (as the result of experimental studies) 

 that a necessary condition of artificial parasitism is a higher osmotic 

 concentration of the fluids of the plant species used as parasite. 

 Harris and Lawrence have carried out an extensive investigation of 

 the problem on Loranthaceous parasites in the Jamaican rain forests, 

 and in a paper now in press have shown that in the case of plants 

 growing under these conditions the parasite is generally but not 



'Shreve, A Montane Rain Forest, Carnegie Inst. Wash. Pub. 199. 



