124 CARNEGIE INSTITUTION OF WASHINGTON. 



Brief reports on the various phases of this work have been made in pre- 

 ceding Year Books. During 1922 and 1923 progress has been made along 

 the following lines: 



Tropical Element in North American Flora. 



Evidence is gradually accumulating that the intrusion and persistence 

 of the West Indian element in the flora of subtropical Florida is due in part to 

 the physico-chemical properties of their tissue fluids. During the winter 

 of 1922, Dr. Harris, assisted by C. W. Crane, made extensive series of deter- 

 minations in southern Florida, extending as far as Flamingo in the Cape Sable 

 region. Here conditions remarkably similar to those investigated in the 

 Jamaican coastal deserts by Harris and Lawrence a number of years ago were 

 encountered. 



Selective Elimination of Species Due to Changes in Salinity of the 



Soil Solution. 



The opening of Jupiter Inlet on the Florida east coast, after it had re- 

 mained closed for several years, has given an opportunity to consider the 

 action of natural selection with respect to sap properties. The considerable 

 areas of fresh-water swamp which will be occasionally touched by salt water 

 had already been studied by Dr. Harris to some extent, and the sap properties 

 of the species which are growing under these conditions are known. Future 

 observations will determine to what extent the elimination of species is 

 dependent on their sap properties, and to what extent the sap properties 

 of other species change with the modification of conditions. 



Other Studies on Natural Vegetation. 



Such measurements on the sap properties of alpine and desert plants as 

 could be made incidentally to experimental work in Utah and Arizona have 

 been carried out by Dr. Harris. The time demanded by experimental 

 studies is rapidly rendering this environmental work difficult, and it will soon 

 be brought to a close as a major project, and be continued only incidentally 

 to experiments under way in the various regions. 



A report on the investigations in the highly saline and other environments of 

 Tooele Valley, Utah, on the southern shore of the Great Salt Lake, reviewed 

 in a preceding Year Book, has been completed for publication. 



Investigations on the Cereals. 



As noted in preceding reports. Dr. Harris has made investigations on the 

 physico-chemical properties of wheat and other small grains in the arid region 

 of the Great Basin since 1920. These studies have been made possible by 

 the U. S. Department of Agriculture with the cordial but informal coopera- 

 tion of the Utah Agricultural Experiment Station and Agricultural College. 



From 1920 to 1922, inclusive, attention was devoted primarily to the 

 change which takes place with the advance of the season when the various 

 varieties are grown with and without irrigation. These studies have, how- 

 ever, involved preliminary comparisons between fall and spring wheats, 

 and general comparisons between the varieties. This phase of the work is 

 now in an advanced stage of preparation for publication. In 1923 the purpose 

 of the work was changed so as to deal more intensively with the differentiation 



