Benedict : New hybrids in Dryopteris 43 



in genera other than Dryopteris, Indeed, several have been re- 

 ported for Asplenhun^ principally in Europe, and in Polysttchum^ 

 and we may expect such genera as Athyrium and others which 

 contain groups of similar associated species to produce crosses 

 when conditions are favorable. 



The fern hybrids known at present are nearly all from temperate 

 regions, but the damp forests of the tropics with their numerous 

 related species and multitudes of individuals would seem to furnish 

 ideal conditions for inter-specific crossing, and it is possible that 

 many plants described as species are really hybrids. But as is 

 noted hereafter, the determination of a hybrid requires a most 

 thorough knowledge of the parent species and all their variations, 

 not only in the herbarium but especially in the field, and until 

 the intensive study necessary to the attainment of such knowledge 

 can be given, the classification of the different forms as species is 

 the only satisfactory method of treatment. 



r 



Fortunately for the study of our native hybrids, one of the 

 commonest of them, Dryopteris cristata x Dmrginalis^ has been ex- 

 perimentally produced, so that its origin is undeniable, and we are 

 justified in assuming that plants which possess the same general 

 characteristics and are similarly intermediate between two known 

 species are also hybrids. A knowledge, therefore, of the general 

 features of D. cristata x marginalis is important in the study of 

 other Dryopteris hybrids. These features may be considered under 



three heads : (i) intermediate character, (2) sterility, abnormality, 

 and greater vigor, and (3) distribution. 



I, The intermediate character of D. cristata x via7ginalis led 

 Dodge and Davenport to suspect its hybrid origin, but a study of 

 numerous specimens of the hybrids shows that they are not all 

 intermediate to the same extent. As one might expect, some plants 

 show greater resemblance to one parent and some to the other. 

 It is interesting to note also that an occasional reverting frond is 

 found which resembles one parent much more than the other fronds 

 on the same plant. In determining whether a suspected plant is 

 intermediate or not, it is necessary to take into consideration sev- 

 eral characters. 



A, The general habit of growth often attracts the attention 

 before the more easily described diagnostic characters can be seen 



