DEPARTMENT OF BOTANICAL RESEARCH. 69 



From the above it is seen that the behavior of protoplasm as a 

 hydrophile emulsion colloid, as previously shown (Carnegie Institu- 

 tion Year Book for 1915, p. 66), may express itself in terms of normal 

 activity. We have here demonstrated, on material from which turgor 

 as a factor in growth is excluded, that the analogy between the behavior 

 of hydrophile emulsion colloids (such as gelatine) and protoplasm in 

 living condition in fact obtains, and that this behavior can express 

 itself directly in alterations in growth-rate. It must, however, be 

 noted that the concentrations are very low as compared with those 

 which produce measurable alterations in the imbibition capacity of 

 non-living emulsion colloids. Protoplasm is, however, a complex of 

 such colloids whose imbibition capacities are probably different among 

 themselves, and are at all events at present unknown. 



ECOLOGY AND PHYTOGEOGRAPHY. 



The R6le of Climatic Factors in determining the Distribution of Vegetation in the 



United States, by Burton E. Livingston and Forrest Shreve. 



A joint study of the distribution of climatic conditions and the dis- 

 tribution of vegetation has been in progress for eight years. The aim 

 has been to secure a basis upon which to enter into an examination 

 of the correlations between the distribution of climatic factors and of 

 plants, and to ascertain some of the climatic controls which are opera- 

 tive in limiting distributions of vegetation and of individual species. 

 Prior to the present year the progress of this work has consisted in 

 the collection and elaboration of data by both of the authors. 

 New modes of expression of climatic data, as related to plants, have 

 been devised, and are described in the Year Book for 1915. A new 

 subdivision of vegetational areas for the United States has been 

 worked out, as described on another page, and some new methods of 

 charting the relative dominance of different growth-forms of plants 

 have also been worked out in connection with this study. 



During the present year the assembling of climatic and vegetational 

 data has been completed, the correlations which formed the object of 

 the work have been made, and the material has been brought to an 

 advanced stage of readiness for pubUcation. 



Some 38 climatological features have been elaborated, chiefly from 

 the published observations of the United States Weather Bureau, 

 using from 134 stations in some cases to over 1,000 stations in others. 

 The number of features worked out for each of the major climatic 

 factors is as follows: Temperature, 12; precipitation, 7; evaporation, 4; 

 moisture ratios (ratio of precipitation to evaporation), 5; vapor- 

 pressure, 2; humidity, 3; wind, 1; sunshine, 1; moisture- temperature 

 indices (the moisture ratio times a temperature datum), 3. 



One of the most carefully elaborated of the cUmatic features is the 

 length of the frostless season, which has been determined for 1,200 



