146 



R. H. RICHENS 



intermediate between U. carpinifolia and U. glabra] 61b has the characteristic leaf shape 

 of U. carpinifolia sens. str. 



Of the remaining samples, two, 50 and 62, agree in being very narrow-leaved types 

 with low asymmetry. In other respects they are remote from one another, 50 having 

 much fewer teeth. Both these samples differ from la in their low asymmetry and fairly 

 high obversity. These samples are therefore relegated to separate subgroups Villa and 

 Vlllb of a single group. Both appear to pertain to U. carpinifolia, and 62 approaches 

 U. coritana var. angustifolia Melville, though it is less asymmetrical than the type. Sample 

 50 is remote from any of the described microspecies. 



Another isolated type is the smooth-leaved sample 81. It comes nearest to Id and 

 le but differs in the very long petiole and rather low asymmetry. It is relegated to a separate, 

 group IX. It obviously pertains to U. carpinifolia, but corresponds to none of the described 

 microspecies. 



A much more extreme type, and, in fact, one of the most distinctive elms collected 

 in the whole area, is sample 32. Its outstanding characteristics are its very long petiole 

 and extreme obversity. In addition, the veins leave the midrib at a narrow angle and 

 show a tendency to curve inwards at the apex. This elm, which was only encountered 

 in the vicinity of Buntingford, appears not to have been previously recognised. It could 

 possibly be accommodated under U. carpinifolia, but is very remote from the other 

 smooth-leaved elms. It is classed here as the sole representative of group X. 



It is convenient, at this point, to refer to those isolated samples which have not been 

 referred here to any group, mainly because of the possibility that further collection will 

 reveal intermediate types connecting them with the groups already recognised. Sample 

 04 has been discussed already; 12 is close to la but has fewer teeth; 27 is fairly close 

 to If but is considerably narrower. Sample 30 would come into Ila were it not for its 

 shorter petiole, while it is only the high tooth number that separates 28a from III. Sample 

 34 approaches IV but has a longer petiole; like 26 in this group, it has the leaf shape 

 characteristic of U. carpinifolia sens. str. 



Elm 17b is a small-leaved type. Although so small, its tooth number is not pro- 

 portionally low, and its other salient characteristics, long petiole, low asymmetry and 

 high obversity, may be consequences of its reduced size. It is possible that such small- 

 leaved types occur sporadically in each of the groups recognized. In the meanwhile, 

 17b will not be placed in a separate group. 



An unusual combination of characters is found in 86a, in which the narrow scabrous 

 leaves have a high tooth number, short petiole and low obversity. It is possible that 

 this sample may eventually link up with Id so that, for the time being, it is not allocated 

 a group of its own. 



The last sample to require consideration is 06. This is a type with smooth, moderately 

 broad leaves, few teeth and shortish petioles. Its nearest subgroup is la, but it has the 

 proliferating habit characteristic of U. plotii Druce. Typical U. plotii, however, which 

 has rather longer petioles, was not collected in the area studied, and sample 06 is probably 

 to be regarded as a form intermediate between U. plotii and U. carpinifolia. It is relegated 

 here to group XI. 



The bearing of these observations on the problem of specific discrimination in Ulmus 

 is somewhat intricate. In general, the demarcation of species within a genus depends on 

 the recognition of discontinuities in the range of variation shown by the group as a 

 whole. It is customary, in sexually-reproducing organisms, to distinguish between species 

 proper and hybrids, the latter being usually few in numbers compared with the putative 

 parent species. The genus Ulmus, however, is atypical in that, while U. glabra regularly 

 reproduces by seed, U. carpinifolia and U. procera normally reproduce vegetatively,though 



