STUDIES ON ULMUS 



1. THE RANGE OF VARIATION OF EAST ANGLIAN ELMS 



By R. H. RicHENS 

 Commonwealth Bureau of Plant Breeding and Genetics, Cambridge 



The English elms have been taxonomically recalcitrant for over three hundred 

 years. The present paper is an attempt to see how far a biometric analysis based on a 

 systematic sampling survey can be used to provide an objective description of the range 

 of variation encountered in the genus and to elucidate some of the taxonomic and other 

 problems that it presents. 



Sampling Technique 



The area surveyed was major square 52 of the Ordnance Survey national grid; the 

 corners of this 100 km. square are located respectively in the vicinity of Stamford, Wymond- 

 ham, Amersham and Maldon (cf. Fig. 1). This area is one of crucial importance as far 

 as the systematics of Ulmus is concerned. The sampling units within the major square 

 were the hundred 10 km. squares composing it. A site in each minor square was selected 

 beforehand for subsequent visiting. The sites chosen were ancient parish boundary 

 hedges with trees and within convenient access from a road. Such sites can be located 

 on the first edition of the 6 inch to a mile Ordnance Survey maps. These mark both 

 trees and parish boundaries. Many of these sheets were issued before the taking effect 

 of the Divided Parishes Acts of 1876 and 1882, and these can usually be taken as giving 

 a reliable indication of the course of the medieval boundaries. The later sheets must be 

 used with more caution lest recent boundaries of no historic standing should be selected. 



Boundaries are utilized because these are extremely permanent features of the 

 countryside and are only alterable by Act of Parliament. It seems reasonable to suppose 

 that the trees growing in them will usually represent the descendants of trees growing 

 on the same site at a considerably earlier period. This supposition is supported by the 

 fact that, in some cases, boundary trees mentioned in Anglosaxon charters are still repre- 

 sented today by the same species marking the same point in the boundary (cf. Stonor, 

 1951). 



Collection is deferred till 1 June and continued till 30 September. Sampling earlier 

 in the year is inadvisable since the leaves are apt to be immature. Each preselected 

 locality is visited and the relevant hedge examined for elms. Ten leaves are then collected 

 from a representative tree, or, if more than one evidently dissimilar elm is present, ten 

 leaves from each sort. The leaves are picked from dwarf shoots growing from major 

 branches, taking care to avoid suckers, lammas shoots, and trees heavily attacked by 

 insect pests. The leaves chosen are the subdistal members of the dwarf shoots. 



Biometric Technique 



Each leaf is measured for five quantitative characters : lamina breadth/lamina 

 length; the number of teeth; petiole length/lamina length; the degree of basal asymmetry; 

 and the tendency towards obverse configuration. Lamina length is measured on the 

 longer side of the leaf. Breadth is taken as maximum breadth. Minor teeth are counted, 

 not the major teeth on which they are superposed. Basal asymmetry is calculated from 



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