SEXUAL AFFINITY 287 



(iii) If the flowers of the parents are dissimilar in colour, those 

 of the variety-hybrids produced by crossing them are generally 

 diversely mottled with both colours, in separate patches, and not 

 blended into one uniform tint. 



Other peculiar characteristics, especially of the fruits of the 

 parents, are often found unblended in varying proportion in the 

 offspring ; hybrids in which the characters of the parents are 

 found thus unmixed are termed ' mosaic-hybrids.^ 



(iv) The power of seed-production is strong and their seedling 

 offspring is generally very vigorous. 



It has been found in a large number of instances that the 

 pollen of one plant cannot impregnate the ovules of another 

 mdely differing from it, but we have no means of determining 

 beforehand whether any two particular species will cross suc- 

 cessfully ; nothing save actual trial will decide. 



Many examples are known where cross-fertilisation does take 

 place between different species of plants, as for example, between 

 the raspberry and blackberry, wheat and rye, different species 

 of strawberry {Fragarid) and various species of Pelargonium, 

 Dianthus, Narcissus, Digitalis, Viola, Gladiolus, Begonia and 

 many other ornamental flowering - plants. Cross - fertilisation 

 between distinct species of plants is termed hybridisation, and 

 the progeny of such crossing are termed hybrids : when the 

 species crossed belong to the same genus, the progeny are some- 

 times designated species-hybrids, to distinguish them from genus- 

 hybrids, or bigeneric hybrids the progeny of species belonging to 

 different genera. 



Few or no crosses are known with certainty between plants 

 belonging to different Families or Orders ; even genus-hybrids 

 are comparatively rare. 



Generally the more nearly allied the species are the more 

 readily do they hybridise. 



The species belonging to certain Orders seem naturally in- 

 clined to hybridisation ; especially is this true of the Composites, 



