DEPARTMENT OF BOTANICAL RESEARCH. 103 



results of European investigations and to interpret them in the light 

 of recent advances. 



The concept is advanced that the climax community typical of each 

 climatic region is the result of a definite organic development, and hence 

 is a basic unit of vegetation, i. e., a formation. This has furnished a 

 new basis for the analysis of vegetation, and makes available a natural 

 method for the classification of the plant communities of the world. 

 It also makes it possible to interpret all the structures of vegetation 

 in terms of successional development, and to discover in existing vege- 

 tation organic relationships which have hitherto been obscure or 

 unknown. A striking advance has been made in correlating vegeta- 

 tion and climate, and this promises to throw a flood of light upon the 

 relations of climate and vegetation in the geological past. Progress 

 has been made to a stage in which it is possible to sketch the climax 

 formations of the various geological periods and to relate them in a 

 developmental series. 



An exhaustive analysis has been made of the initial, ecesic, and 

 stabilizing causes of unit successions, and especial attention has been 

 given to the orientation of topographic, climatic, and biotic processes. 

 As a result, it has been possible to extend and refine our present knowl- 

 edge of the structure of vegetation and to propose a purely develop- 

 mental classification of plant communities. Out of this has come a 

 new conception of the interrelations of contiguous climax formations 

 and their correlation with past and future climates. 



The Relationships and Distribution of the Cactacece, by N. L. Britton 



and J. N. Rose. 



Field-work in this investigation yv&s continued by Dr. Britton in 

 Porto Rico and islands adjacent in February and March, including 

 successful exploration of the small islands Desecheo and Mona, in the 

 Mona Passage between Porto Rico and Santo Domingo, and the cacti 

 of both these islands vrere collected and transmitted to Washington 

 and to the New York Botanical Garden; one of the most interesting 

 results was the recognition of the long-lost Cactus monilijormis of 

 Linnaeus. Important knowledge on the distribution of species was also 

 obtained. Dr. J. A. Shafer explored the island of Vieques, on behalf 

 of the New York Botanical Garden, and obtained specimens of the 

 cacti of that island. At the end of Maj^ Dr. Britton again visited 

 Bermuda and studied cacti in cultivation there. The collection of 

 cacti made by Mr. John G. Sinclair during the winter in Colombia, 

 South America, supplied valuable information concerning the species of 

 that region. The explorations of Dr. MacDougal in Arizona, Cali- 

 fornia, and Nevada during the year added much to our knowledge of 

 species and their distribution. Additional information and specimens 

 concerning the cacti of Panama were received from Mr. H. Pittier. 



