268 



P. F. YEO 



At one locality E. vigursii itself appears to have been modified by introgression from 

 another tetraploid species. 



Four other hybrids analogous to E. vigursii are described. In addition, there occur 

 hybrids of similar origin, but in which there is merely introgression of characters with 

 no apparent ecological significance, and no isolation of hybrids from the diploid parent. 



Reported cases are mentioned of diploids in four other genera whose immediate 

 ancestry includes a diploid and a tetraploid; in two cases the occurrence was natural. 



In spite of the abundance of intermediate individuals derived from the kind of 

 hybridisation described, the two original populations cannot merge into one, owing to 

 the difference of chromosome number. 



Acknowledgments 



I am grateful to Professor T. G. Tutin for supervising this work, and for reading 

 the manuscript of the paper, and to the Research Board of the University College of 

 Leicester for the provision of a Research Scholarship and for paying my travelling 

 expenses. Dr. S. M. Walters and Dr. E. F. Warburg also greatly helped in the improve- 

 ment of the manuscript. Mr. J. S. L. Gilmour kindly read the part referring to " demes." 



I am indebted to Mr. N. D. Simpson and to the Curator of the Cambridge University 

 Herbarium for the loan of collections, and to the authorities at the Kew and British 

 Museum (Natural History) Herbaria for facilities. 



Appendix : Localities for E. vigursii 



Cornish records are grouped according to the floristic divisions of Davey (1909). 

 The following abbreviations are used to indicate the sources of records : BM, the British 

 Museum (Nat. Hist.) Herbarium; CGE, Cambridge University Herbarium; DF, Davey's 

 (1909) Flora of Cornwall', K, the Kew Herbarium; PM, Pugsley's (1930) monograph; 

 S, Mr. N. D. Simpson's herbarium. 



All specimens collected by me are in my herbarium, and most gatherings are also 

 in the herbaria of the University College of Leicester and Cambridge University. 



Records of E. anglica and E. micrantha from localities for E. vigursii are also included. 



V.c. 1. W. CORNWALL 



District 7 : Lizard Downs, Salmon, 1926 (BM). 



District 6 : edge of Newlyn Downs between Garland and Zela Hill, Yeo, 1953 (locality for E. 

 micrantha, Yeo, 1953). 



District 5 : Perranzabuloe, Bahington, 1839 (CGE), (locality for E. micrantha, Babington, 1839 

 (CGE)); Reen Common, Perranzabuloe, Vigurs, 1907 (CGE), (locality for E. micrantha, Vigurs, 

 1907, (CGE)); Ventongimps, Perranzabuloe, Rilstone, 1918 (K); Goonhavern, Davey, 1906 

 (CGE), Tresidder, 1909 (CGE), (locality for E. micrantha, Tresidder, (DF), Ribtone, 1922 

 (PM)); Mill Down, Goonhavern, Thurston, 1916 (K); Polgoda Downs, Lousley, 1936, (K). 

 Yeo, 1953; Newlyn Downs, Thurston, 1916 (K); Shepherds, Druce, 1917 (BM); Zela Hill, 

 Yeo, 1953; Droskyn Point, Perranporth, Thurston, 1916 (K), Yeo, 1953; dowTis near Perran- 

 porth, Rilstone, 1918 (CGE); Quintrell Downs, near Newquay, Vigurs, 1907 (K), (locality for 

 E. micrantha, Vigurs, (DF), Hume (PM)); Connor Downs, (DF); Porth Towan, Davey, 1905 

 (CGE). 



District 4 : St. Issey Downs, near Padstow, Riley, 1906 (K), (locality for E. micrantha, Riley, 1906 

 (K)). 



V.c. 2. E. CORNWALL. 



District 3 : Helman Tor, Rilstone, 1923 (? E. vigursii); Cheesewring Down, Minions, Rilstone, 

 1920 (BM); opposite Duchy Terrace, Minions, Thurston, 1923 (K), (Minions is a locality for 

 E. micrantha, Thurston, 1923, (K), Yeo, 1953, and for E. anglica, Yeo, 1953); slopes of Caradon 

 Hill. Rilstone, 1920 (BM) and Yeo. (Pensilva). 1953, (locality for E. micrantha, Yeo, 1953); 

 Herod Down, near Pillaton, Jenkins (DF). 



