42 



Ecology 



Mr. Taylor has continued his studios upon the vegetation of 

 Long Island, and in cooperation with Major Barrington Moore, 

 upon that of Mt. Desert Island, Maine. The comparison of the 

 soil and climatic factors of these widely separated islands, both of 

 which support the pitch pine, is yielding instructive information 

 upon the forest possibilities of both localities. 



The Vegetation of Long Island which it was originally intended 

 should be issued as one Memoir volume, has been, with my con- 

 sent, divided into separate parts, such as grasslands, forests, coast- 

 al marshes, etc. Each of these present special problems, often 

 of considerable economic importance, and it seems best to issue 

 these reports when completed. The first on The Vegetation of 

 Montauk: A Study of Grassland and Forest will be ready for 

 the press early in 1923. Further details of this may be found in 

 the appended Report of the Curator of Plants. 



Genetics 



Experiments by the director of the Garden on the effect of 

 radium rays on germ cells, the beginning of which was noted in 

 my preceding annual report, were continued, in cooperation with 

 Dr. A. F. Blakeslce, Carnegie Station for Experimental Evolution, 

 Cold Spring Harbor, L. I. In these experiments ovaries of young 

 flower buds of the Jimson weed or Thorn apple (Datura Stramon- 

 ium) of pedigreed stock inbred for about twelve generations by 

 Dr. Blakeslee, were exposed to gamma rays from radium emana- 

 tion contained in a sealed glass tube. The exposure was made 

 by inserting the tube, which was about the diameter of a large 

 needle, into one of the four cells of the ovary. Numerous ex- 

 posures were made for varying periods of time with a varying 

 strength of radiation. An exposure of ten minutes with a 

 strength of 13 microcuries was followed by a great increase in the 

 percentage of mutant forms. The maximim was 33.33 per cent, 

 for the ovules in the cell into which the radium tube was inserted. 

 16.07 P er cent - ror the cell farthest away, and an average of 16.96 

 per cent, for all four cells. The average percentage of mutants 

 in the same stock for four years (1919-1922), without experi- 



