Fig. 3. Northern, limit of Dryopteris horreri in Europe, 



south of England in which this fern is present. The pH of the soil has not yet been 

 investigated and, therefore, no definite information on this point is available. Of the 

 several localities in Norfolk and Suffolk, in which this fern has been found, none is 

 markedly alkaline and it is probable that D. horreri occurs in many other localities which 

 have not yet been recorded. Lee (1933) reports that D. horreri is common in Ayrshire 

 and a few localities in the south-east corner of Kirkcudbrightshire. The latter localities 

 have been confirmed by representative specimens collected in 1951 by P. Taylor. 

 It therefore seems most improbable that this fern is entirely absent from Wigtown 

 although there are, as yet, no records. The apparent absence of this fern from Caithness, 

 East Sutherland and East Ross as well as from North Aberdeenshire seems surprising 

 and is probably due to the failure of botanists to distinguish D. horreri from D. filix-mas, 

 since the latter is recorded from these vice-counties. The apparent distribution in Ireland 

 is also unexpected and a similar explanation probably applies here. 



Detailed work on the ecology of this species may prove interesting since D. horreri 

 is usually found in damper and more shaded situations than D. filix-mas, although not 

 invariably so. It is hoped that this will be touched on in the investigation of the distri- 

 bution of polyploid races which is now being undertaken. Manton (1950, 59) has 

 demonstrated diploid and triploid strains ; it will be interesting to see if there are any 

 other chromosome races and also if chromosome number has any bearing on the ecological 

 requirements. 



Local populations of D. horreri may be almost pure, being in fact clonal, and may 

 exhibit differences in small details of the characters which are given above in the para- 

 graph on description, from populations of other localities. Owing to the absence of 

 gametic fusion, gene exchange does not occur, and hence small genetic changes within 

 a plant are retained throughout succeeding generations and local stands may exhibit 

 remarkable similarity among themselves but dissimilarity from other stands. It is important 

 to remember these facts when identifying plants of D. horreri. Hybrids between D. horreri 



