ECOLOGY. 311 



be fully studied. Since reciprocal transplants are made between related 

 forms, the results will also be directly applicable in fundamental studies on 

 the taxonomy of this genus of shrubs. Similar work is under way with 

 Asclepias and it is intended that the results from both series of investigations 

 shall supplement those of other studies in experimental taxonomy, as de- 

 scribed above. Further work has been done on the ecology, distribution, 

 and growth of Asclepias subulata, and the results of pruning experiments are 

 now becoming available. The cortex of the stems and especially that of the 

 younger portions has been found to contain the best rubber, as well as much 

 the largest amount, A number of other species have been analyzed for 

 rubber during the year, especially the spurges, but none have shown a suffi- 

 cient quantity to warrant further consideration. 



Latex and Laticiferous Tissue, by Frances Long. 



The histological study of laticiferous tissue in a wide range of genera has 

 been continued, and seedhngs have been grown to permit a study of the 

 origin of the three types of latex vessels. In this connection, particular 

 attention is being given to the storage of starch and resins in latex-bearing 

 plants and its relation to the milk tubes. An endeavor is also being made to 

 determine the fate of the latex in the various organs at the close of the season. 

 Several species of Asclepias, Euphorbia, Campanula, and Cichorieoe are being 

 grown under different conditions of water and light in the hope of disclosing 

 factors that produce variation in the amount of latex and its rubber-content, 

 both under control and in nature. 



Experimental Vegetation, by F. E. Clements and J. E. Weaver. 

 Studies in experimental vegetation begun in 1919 were continued during 

 1923 with the primary purpose of obtaining another season's results to 

 compare with those of previous years and also to measure by phytometers 

 the differences indicated by instruments and the behavior of native plants 

 (cf. next two sections). As heretofore, the stations maintained extended 

 from the subcHmax prairie at Nebraska City to true prairie at Lincoln, 

 Nebraska, mixed prairie at Phillipsburg, Kansas, and short-grass plains at 

 BurUngton, Colorado, At Lincoln the local stations ranged from xerophytic 

 gravel-knoll, through high prairie, low prairie, and salt-flat, to swamp. 

 During 1922 the average germinations under all methods of planting, viz, 

 surface sowing, trench, and denuded quadrat, were 75, 74, 67, 63, and 44 

 per cent at Lincoln (low and high prairie), Nebraska City, Phillipsburg, and 

 Burhngton, respectively. EstabUshment in the same sequence of stations 

 was 50, 62, 46, 39, and 26 per cent. The average losses of all plantings for 

 the past 3 years during the fall and dry winter (1922-23) were 16 per cent at 

 Lincoln (high prairie), 29 per cent at Phillipsburg, and 46 per cent at Bur- 

 lington. In concluding the work, tables are being compiled showing for the 

 several stations the average percentage of germination for the three or four 

 years and the average percentage of establishment, as well as the percentage 

 of survival at the end of each year for the several methods of planting and 

 transplanting. For example, in denuded quadrats at Nebraska City, 

 planted in 1920, there was 100 per cent survival at the end of the first season, 

 90 per cent at the end of the second, but only 80 per cent by the end of the 

 third year. Average germination for 3 years gave 81, 70, and 42 per cent, 

 respectively, at the true and mixed prairie and short-grass plains stations. 



