308 



J. K. MORTON 



Method 



In the first place an indication of the nature of the colonies at Marsden and Blackhall 

 Rocks was obtained by recording each plant under the following categories : — O. spinosa, 

 O. repens, intermediate plants approaching O. spinosa, intermediate plants approaching 

 O. repens, and completely intermediate plants. The results of this estimation are shown 

 in Table 1 below. 



Table 1. 



O. repens 



Intermediate plants approaching O. repens 

 Completely intermediate plants 

 Intermediate plants approaching O. spinosa 

 O. spinosa 



Marsden 

 /o 

 31 

 5 

 11-5 

 34-5 

 18 



Blackhall 



o/ 



/o 



27-3 

 0-7 

 12 

 32 

 28 



Apparent composition of the colonies based on visual characterisation of individual plants 



Later, a more precise method was used, in which the various characters of the indivi- 

 dual plants were each given a numerical value, the character index. The sum of the 

 character indices for each plant gives the character sum index. This is highest in plants 

 approaching most closely to O. spinosa and lowest in those approaching most closely to 

 O. repens. The following are the characters which were scored and the method used in 

 their assessment : — 



(a) Leaf Index. This was obtamed by dividing the length of the terminal leaflet 

 by the greatest breadth. An index of from 0 to 1-8 was scored as 1, from 1-9 

 to 2T as 2, and 2-2 upwards as 3. There is considerable overlap between the 

 two species in respect of this character, and the dividing points in the method 

 of scoring were selected as being the most realistic, after examination of colonies, 

 belonging to both species, from many parts of the country. 



Fig. 1. Diagram of Ononis Flower (v. ith standard removed) to show 

 the method of measuring the lengths of wing (a) and keel (b). 



(b) Flower Index. This was obtained by dividing the length of the wings by the 

 length of the keel, the measurements being taken along the axes shown in Fig. 1. 

 An index of 0 to 0-96 was scored as 3, 0-97 to 103 as 2, and 104 upwards as 1. 



