VARIATION IN THE NUMBER OF SEEDS PER 

 POD IN THE BROOM, CYTISUS SCOPARIUS 



DR. J. ARTHUR HARRIS 

 Carnegie Institution of Washington 



While at Wood's Holl in August, 1907, I collected 

 about 100 pods each from a series of 23 bushes of the 

 broom Cytisiis scoparius. On a vacant lot not far from 

 the Marine Biological Laboratory the plants were grow- 

 ing vigorously, completely covering the space with 

 bushes, many of which were higher than a man's head, 

 and with stalks about an inch in diameter at the base. 

 The material was gathered for an investigation of the re- 

 lationship between the number of ovules formed and the 

 number of seeds developing per pod. But when the 

 counting was taken up the determination of the number 

 of aborted ovules proved so difficult that I feared the 

 results would be untrustworthy and gave up the project. 

 While working over the data I noticed that Pearson 1 has 

 recorded a series of countings of broom from an English 

 locality, and it has seemed worth while to compare the two 

 lots of material. 



Many biologists have held the opinion that changed 

 conditions of life, such as may be supposed to prevail 

 when a species is transferred from one habitat to another, 

 imply an increase in variability. The theories concern- 

 ing the reason for this phenomenon need not be discussed 

 here. I think the general idea will be familiar to all. I 

 think about the only attempts to determine quantitatively 

 whether there is any increase in the variability of a 

 species when introduced into a new habitat are two studies 

 by Bumpus. He first considered the variability of the 

 egg of the introduced sparrow 2 and concluded that it is 

 decidedly more variable in the United States than in its 



1 Pearson, K., and others, Phil. Trans. Boy. Soc. Lond., A, 197, 335, 1901. 

 s Bumpus, H. C, "The Variations and Mutations of the Introduced 

 Sparrow," Biol. Lect. Mar. Biol. Lab. Wood's Holl, 1896-97, 1-15. 

 350 



