316 



J. K. MORTON 



do not hybridise. The results obtained, from both the Marsden and the Blackhall Rocks 

 colonies, show that the two species cannot be clearly separated here, and that a high 

 proportion of intermediate plants occurs in both localities. Further, the analysis of each 

 character shows that characters of an intermediate nature tend to be associated in the 

 same plant, and do not occur at random throughout most of the individuals in the colony. 

 Thus it may be concluded that the range of variability, in the two populations studied, 

 is due mainly to hybridity between the two species, and is not due to variation within the 

 species themselves. 



Acknowledgments 



The writer's thanks are due to Professor H. G. Baker and Dr. B. J. Harris for their 

 advice on the presentation of the results. This has greatly facilitated the preparation of 

 the paper for publication. 



REFERENCE 



ANDERSON, E., 1949, Introgressive Hybridization. New York. 



Key to Symbols Used in the Pictorial Scatter Diagrams 



Vertical axis = leaflet length (in mm.). Horizontal axis = leaflet width (in mm.). Each plant is represented 

 by a dot. Characters are denoted by arms ; presence of a character by a full length arm, an intermediate 

 condition by an arm of half the length, and absence of a character by omission of the arm. 



1 - leaflet tip habit 



^— stem colour /-line of hairs 



\ - spines. 



Thus a plant in which all the characters are present will appear as 

 are absent as — # 



and one in which all the characters 



