164 BLASTOGENIC VARIATIONS. 



Roth, in the same way from D. purpurea and D. am- 

 bigua (grandiflora) . . . D. ambigua has also been 

 crossed with D. purpurea and with D. lanata, in each 

 case yielding hybrids which also occur wild." 



Rolfe also records that Wichura succeeded in raising 

 artificially no less than eight hybrid willows identical 

 with those which had long been known in the wild state, 

 and Linton has added at least six others. For instance, 

 Salix rubra was obtained by crossing 8. purpurea with 

 the pollen of S. viminalis. 



Kerner is of the opinion that species may be produced 

 by hybridisation. In his " Natural History of Plants " 

 he gives instances of these hybrid races. To quote 

 Rolfe, " A hybrid between Medicago falcata and sativa, 

 known as M. media, is widely cultivated as a fodder 

 plant, and is propagated from seed. Salvia betonicce- 

 folia, a hybrid from 8. nemorosa and nutans, is as com- 

 mon as its parents in grassland in Central Hungary. 

 Betula alpestrisj a hybrid between B. alba and nana, is 

 abundant in the Jura, Scandinavia, and in North Russia, 

 here and there whole copses of it being found. Nigri- 

 tella suaveolens, a hybrid between N. angustifolia and 

 Gymnadenia conopsea, is abundant in some Swiss locali- 

 ties, hundreds of plants sometimes occurring in a single 

 meadow. Hybrids between the Primrose and Cowslip 

 occur in thousands in upland meadows in the Eastern 

 Alps." 



Again, in some localities in the Tyrol the hybrid 

 Rhododendron intermedium exists side by side with its 

 parent forms, R. ferrugineum and R. hirsutum, it 

 sometimes being commoner than they are. Also it 

 seeds freely, and comes true to seed, and so fulfils all 



