STUDIES ON ONONIS IN BRITAIN 



309 



(c) Occurrence of spines. A spinous condition such as is normal to O. spinosa was 

 scored as 3, absence of spines as 1, and an intermediate condition as 2. 



Fig. 2. Stem pubescence in Ononis. 

 Left : uniform pubescence in O. repens. Right : band of hairs in O. spinosa. X 2. 



(d) Occurrence of a band of hairs on the stem. A distinct band of hairs, such as is 

 normal to O. spinosa, was scored at 3, uniform pubescence as 1, and an inter- 

 mediate condition as 2. (See Fig. 2). 



(e) Stem colour. O. spinosa normally has a very dark red stem, a condition which 

 was scored as 3. O. repens usually has a green stem sometimes tinged with red. 

 Such stems were scored as 1, and an intermediate condition as 2. 



(f) Habit. O. repens has long underground rhizomes and straggling aerial shoots. 

 O. spinosa has an erect bushy habit and no rhizome. The O. repens condition 

 was scored as 1, the O. spinosa as 3, and intermediates as 2. 



Fig. 3. Typical terminal leaflets of O. repens (left) and O. spinosa (right). X 2. 



(g) Leaflet Tip. The leaflet tip of O. spinosa normally has an acute point, whilst 

 that of O. repens is obtuse and rounded, or even emarginate. The former con- 

 dition was scored as 3, the latter as 1 and intermediates as 2. (See Fig. 3). 



Thus the character sum index of a plant with all O. repens characters would be 

 7 and one with all O. spinosa characters, 21. 



The Structure of the Colonies 



The normal range of variation, even in pure colonies, produces individual plants 

 of O. repens with slightly higher scores, and of O. spinosa with slightly lower scores, but 

 this variation is by no means sufficient to cause any overlap in the character sum indices. 

 This is clearly shown by the histograms in Figs. 4A to D in which two pure colonies of 

 each species are scored, and in which the histograms for each species are separated by at 

 least 5 units. This is in contrast to the position in the hybrid colonies at Marsden and 

 the Blackball Rocks, where the histograms (Figs. 4E and F respectively) show an unbroken. 



