208 



CYTOGEXETIC STUDIES IX DRYOPTERIS SPIKULOSA : I 



in the hybrids. Spore sowings have not confirmed this and the apparent intergrading is 

 probably not a result of introgression but arises from the polymorphism present in D. 

 dilatata. A detailed c\tological survey of mixed populations could give further informa- 

 tion. An alternative explanation of the appearance of mixed populations may simply 

 be the effect of matrocliny; Chandler (1948) working on the morphology of Dryopteris 

 hybrids in X. i\merica does suggest that this may occur in the wild. In the experimental 

 h^'bridisation between species of the D. spinulosa complex reciprocal crosses have been 

 made without any e\'idence of matrocliny; in almost evers' s^Tithesised triploid there has 

 been evidence of the diploid involved, irrespective of whether the diploid was the male 

 or female parent. This could be explained by gene dosage, each triploid possessing 

 tudce the genome of the diploid present, and would not disccunt matrocliny as a possibility 

 in tetraploid hybrids. 



(7) SUM^L\RY 



Qtological observations have been made on the species and species-hybrids, both 

 wild and synthesised, in the Dryopteris spinulosa complex as represented in Europe (see 

 Table 2 and Fig. 11). 



There are three tetraploid species in the complex, namely D. cristata, D. spinulosa 

 and D. dilatata, all of which are allopolyploids. At least four ancestral diploid species 

 would be required to account for the origin of these triploids. One of the ancestral 

 genomes is common to D. cristata and D. spinulosa, and another is common to D. spinulosa 

 and D. dilatata. 



Chromosome pairing in synthesised hybrids suggests that the common ancestor of 

 D. spinulosa and D. dilatata is now represented by two^ distinct diploid forms of " D. 

 dilatata " ; one is found in Britain and on the continent of Europe and the other on the 

 island of Madeira. It is suggested that these forms should be recognised as subspecies 

 of a single diploid species which is additional to the pohploid complex. The nomenclature 

 and taxonomic description must be left for discussion in a later paper. These diploids 

 differ slightly in their cytological behaviour w^hen hybridised with the tetraploid species 

 D. spinulosa or D. dilatata, indicating that there is differentiation within the diploid 

 genome resulting in a loss of chromosome homolog\'. 



Reciprocal crosses between species in different grades of ploidy have been made 

 without difficulty or e\*idence of matrocliny. 



(8) Acknowledgments 



I am indebted to Professor I. Islanton for her supervision of this work, the supply 

 of material and criticism of the manuscript. Thanks for material and discussion on the 

 taxonomy of the complex are due also to Mr. A. H. G. Alston and for further suggestions 

 to m.y coUeagues at Liverpool. 



REFEREXCES 



CH.\XDLER, A., 1948, Dnopteris Hybrids, Amer. AfjciL Nat., 40, 763. 

 CHRISTEXSEN, C, 1905-6, Index Filicum. Copenhagen. 

 , 1913-16, Irdex Filicum, Supplementum I. Gspenhagen. 



CEIANE, F. \\ ., 1955, Comparative study of diploid and tetraploid spores of Dryopteris dilatata from 



Britain and Europe, Watsonia, 3, 168-169. 

 DRUERY, C. T., 1912, British Ferns and their varieties. London. 

 HOFF\L\NX, G. F., 1795, Deutsche FL, 3, 7. 

 HYDE. H. A. & WADE, A. E., 1948, Welsh Ferns. Cardiff. 

 JACQUIX, N. J., 1764, Observationum Botanicarum, 1, 45. 

 LINXAEUS, C, 1753, Species Plantarum, 1090. 



