136 HYBRIDISING AND CROSS-BREEDING. 



by crossing two pure species belonging to different genera. Ex- 

 amples : PJwjus irroratus, Philagera Veitchii, Sericobonia ignea 

 (Libonia Penrhosiand), and Calanthe Veitchii. 



Bigeneric Half -breeds are plants obtainable by crossing 

 varieties of two species belonging to different genera. 



Hybrids or Mules * are the products of two species. Ex- 

 amples : t Rhododendron altaclarense, R. hybrid- maximum, 

 Clematis Hendersonii, Cypripedium Harrissianum, C. Sedeni, 

 Cattleya Exoniensis, Calanthe Veitchii, Lcelia flammea, Del- 

 phinium formosum, <&c. 



Half-breeds or Mongrels are the 'products of two varieties of 

 pne species. Examples : Many Primulas of the P. sinensis, 

 P. auricula, or P. vulgaris sections; many Peaches, Plums, and 

 other cultivated fruits.J 



Graft Hybrids are the results sometimes produced by 

 uniting two species as scion and stock. Examples: Cytisus 

 purpurascens (= C. Adami). {See Cytisus.} 



Graft Half-breeds. These are produced by grafting varieties 

 of a species together, several instances of intermediate pro- 

 ducts having been observed in Potatoes, &c. 



Seminal Sports are varieties which not unfrequently result 

 from seeds which have not been fertilised by foreign pollen ; 

 indeed, seminal variation, natural selection, or " survival of 

 the fittest," is nature's way of adapting plants to different 

 localities and conditions. Many garden plants have been 



* The word "mule" is frequently used as synonymous for hybrid, and 

 originated at the time when hybrid plants (like hybrid animals) were 

 thought to be universally sterile. It being now known that but a small 

 proportion of hybrid plants are absolutely sterile (M. Naudin thinks about 

 25 per cent), even in the first generation, the word hybrid should be ex- 

 clusively used for the fertile progeny of two species, and the word mule 

 adopted in like manner for such as are sterile. 



t Professor Sachs gives the following definition of the different kinds of 

 hybrids : " According as the union takes place between different varie- 

 ties of one species, different species of one genus, or between two species 

 belonging to different genera, the resulting hybrid may be termed a 

 variety-hybrid, species-hybrid, or genus-hybrid. When a hybrid is made 

 to unite with one of its parent-forms, or with another parent-form, or with 

 a hybrid of different origin, the product is termed a derivation-hybrid." 



It will be seen that inter-crossing is not always conducted regularly 

 according to our table, and in many cases becomes so complicated as to 

 preclude the possibility of classification, except in a large treatise espe- 

 cially devoted to such an extensive and intricate subject. For example, 

 instead of crossing two pure species belonging to different genera, so as to 

 produce bigeneric hybrids, we may employ one pure species and a half- 

 breed or sub-variety of another species and genus, and then we have a 

 bigeneric half-breed intermediate between a true bigeneric hybrid and a 

 bigeneric half-breed ; and so on, in the case of the other classes. 



