586 THE GENESIS OF NEW SPECIES. 



the lower Danube ; Roripa ance2:>s, the hybrid of 2oripa amphibia and R. sylvestris, 

 is met with all over the district forming the basin of the Baltic; Primula digenea, 

 a hybrid derived from Primula vulgaris and P. elatior, grows in its thousands in 

 the upland meadows of the Eastern Alps; Betula alpestris, produced by the crossing 

 of Betida alba and B. nana, is met with in great abundance in the Jura, in Scandi- 

 navia, and in the North of Russia, and here and there entire copses are composed 

 of it; Nigritella suaveolens, a hybrid produced from Gymnadenia conopsea and 

 Nigritella nigra, is so common in the Central Alps, for instance, in the Pusterthal 

 of Tyrol, that hundreds of specimens are sometimes encountered in a single meadow; 

 Primula Salisburgensis, the hybrid of Primula glutinosa and P. minima, is repre- 

 sented by a host of plants on the Tyrolese Alps, as, for instance, on the Muttenjoch 

 and the neighbouring mountains which sejmrate the Gschnitzthal from the Obern- 

 bergthal. 



Several hundreds of other cases of the kind might be mentioned, but the limits 

 of this book will not allow me to do more than give the following names selected 

 from the long list that lies before me : 



Hybrid. Parents. 



Asplenium Germanicmn Asplenium Rutu-muraria x A. septentrionale. 



Calamogrostis acutiflora 0. arundinacea x C. epigeios. 



Carex Boenninghaimana C. paniculata x C. remota. 



Scirpus Duvalii S. lacustris x S. Pollichii. 



Juncus diff'itsus J. effusus x J. glaucus. 



Orchis Dietrichiana 0. trideiitata x 0. ustulata. 



Potamogeton spathulatus P. polygonifolins x P. rufescens. 



Populus canescens P. alba x P. tremula. 



Salix A ustriaca S. grandifolia x S. purpurea. 



Rumex maximus R. aquaticus x R. Hydrolapathum 



Polygonum mite P. Hydropiper x P. Persicaria. 



Cistus Florentimis C. monspeliensis x C. salvifolius. 



Draha Hoppeana D. Fladnizensis x D. Carinthiaca. < 



Roripa stenocarpa R. palustris x R. sylvestris. 



Pulsatilla Hakelii P. patens x P. pratensis. 



Drosera obovata D. longifolia x D. rotundifolia. 



Epilobimn salicifolium £J. alsinifolium x E. montamom. 



Sorbus latifolia S. A ria x S. torminalis. 



Potentilla procumbens P. erecta x P. reptans. 



Mentha nemorosa M. aqua tica x M. sylvestris. 



Pedicularis atrorubens P. incarnata x P. recutita. 



Verbascum rubiginosum V. AustiHacum x V. phcenicewm. 



A canthus spinulosus A. mollis x A . spinosissimus. 



Gentiana Charpentieri G. lutea x G. punctata. 



Primula pubescens P. Auricula x P. hirsuta. 



Vaccinium intermedium T". Myrtillus x V. Vitis-idaea. 



Erica Mackayi E. ciliaris x E. Tetralix. 



Cirsium tataricurn C. canuin x C. oleraceum. 



Lappa pubens L. minor x L. tomentosa. 



Hieracium stoloniflorum H. aurantiacum x H. pilosellceforme. 



The fact that hybrids exhibit every conceivable degree of frequency of occur- 

 rence might lead one to suppose that the rare hybrids were those that had been most 

 recently produced, and that they exist only as isolated plants because they hc.ve not 



