ON VARIETIES IN PLANTS 311 



they include garden and forcing varieties which combine marvellous 

 beauty of form and color with vigor and hardiness (Fig. 126a). Four 

 or possibly five distinct species enter into the ancestry of the group, as 

 shown by the following pedigree. The Hybrid Perpetuals (Fig. 1266) 

 are of mixed ancestry, all being hybrids of the Damask Rose (Fig. 126c) 

 crossed either with Hybrid Bourbon or Hybrid Chinese varieties. 



The hardy, disease-resistant Japanese species, Rosa rugosa and R. 

 wichuriana have entered into the ancestry of some of the best modern roses. 

 Thus, the American Pillar variety is a hybrid between a red Hybrid 

 Perpetual crossed with a hybrid between R. wichuriana and R. setigera, 

 the Prairie Rose of America. Again, the Silver Moon variety is a result 



(Teas derivatives of Rosa chinensis var. odoraiissima 

 IT U -J D 



/ Hybrid --^Rosa galhca 



Hybrid / Chinese ^>^^ (French or Provence 



Perpetuals/ Rose). See Fig. 126<f. 



\\ 



chinensis 



(Chinese Monthly 

 or Bengal Rose). 

 ^flosa damascene 

 (Damask Rose) ^\Rosa centifolia 



(Cabbage Rose). 



FIG. 127. Pedigree of the hybrid tea roses. 



of crossing R. Icevigata, the Cherokee Rose, with a hybrid between the 

 Tea Rose, Devoniensis, and R. wichuriana. These examples will serve 

 to illustrate the composite ancestry of our best roses. The practicability 

 of this method of procuring new varieties has of course been enhanced 

 by the possibility of vegetative propagation. Occasionally valuable 

 varieties have arisen as bud mutations but these usually differ from the 

 parent variety only in some definite character, like flower color or habit 

 of growth. 



In passing it is of interest to note how extensively this method of 

 variety creation has been used by horticulturists, particularly in species 

 whjch are normally propagated by clonal multiplication. The hybrid 

 varieties of the rhododendron rival in diversity and floral magnificence 

 even those of the rose, and like them they have been derived from the 

 mingling of a number of different species. But it is among the Rosacese 

 particularly that horticulturists have found the most favorable subjects 

 for hybridization. It is necessary in this connection merely to mention 

 such familiar examples as varieties of plums, apples, strawberries, and 

 other rosaceous fruits in the production of many of which extensive 

 hybridization has been employed. In seed plants, also, there are many 



