THE CYTOGENETICS OF CAREX FLAVA AND ITS ALLIES^ 



By Elizabeth W. Davies 



University College of Leicester 



I. Introduction 



II. Cytological Technique 



III. Chromosome Numbers 



IV. Hybrids and Hybridisation 



A. Natural Hybrids 



B. Artificial Hybrids 

 V. Discussion 



VI. Conclusion and Summary 

 VII. Acknowledgments 



1. Introduction 



This group of closely allied species included in the section Extensae of the subgenus 

 Carex is represented in Great Britain by : Carex flava L., C. lepidocarpa Tausch, C. 

 demissa Hornem., C. serotina Merat, and C. scandinavica E. W. Davies. The taxonomy 

 of these species has caused difficulty for many years, and, although the chromosome 

 numbers have been investigated by workers in Sweden, Japan and America, there has 

 been considerable discrepancy in their results (see below), and no counts have previously 

 been made on British material. 



Haploid 



Species 



Chromosome Number 



Determined by : 



Date 



C. extensa Good. 



30 



Wulff 



1937 



C. flava L. 



29 



Tanaka 



1942. 1948 





30 



Heilborn 



1939 





30 



Wahl 



1940 



C. lepidocarpa Tausch 



29 



Tanaka 



1942, 1948 





34 



Heilborn 



1924 



"C. oederi Retz " = C. serotina Merat 36 



Heilborn 



1922, 1924. 1928 





35 



Tanaka 



1948 



2. Cytological Technique 



The cytological technique employed throughout this investigation is a modification 

 of the aceto-carmine squash method by the addition of a drop of iron alum. The Carices 

 have exceedingly small chromosomes and hard wiry roots, which make them difficult 

 cytological material. 



The original attempts to count the chromosomes of this genus were made at mitosis 

 using root tips. First embedding and sectioning methods were tried and later the root 

 tip squash technique was used, staining with Feulgen, aceto-carmine, or a combination 

 of the two stains together. However, the results throughout were unsatisfactory, as the 

 cytoplasm was overstained and contained oil globules, while the chromosomes remained 

 faint and aggregated together. Thus the counts were never accurate enough to detect a 

 difference of two chromosomes at mitosis, which is essential when examining a genus 



* Part of a thesis approved for the degree of Ph.D. by the University of London. 



129 



