THE CLASSIFICATION OF PLANTS 221 



difficulty is increased by the ease with which very closely 

 aUied forms hybridize with one another — e.gr., the numerous 

 forms of willows, roses, brambles, and hawkweeds. 



One of our native geraniums is the bloody crane's-bill 

 {Geranium sanguineum). It has a diffusely - branched 

 stem and large purple flowers. G. prostratum, found on 

 the sands of Walney Island, Lancashire, has a dwarf 

 tufted stem, with small flesh-coloured flowers. Is the 

 latter plant a mere variety of G. sanguineum, or is it a 

 separate race ? We cannot say ; we must know how 

 its seeds behave in another environment before we can 

 decide. In the west of Ireland there grow together two 

 saxifrages — Saxifraga umbrosa and S. Geum. According 

 to Babington, these are distinct species ; according to 

 Clement Reid, they are divergent forms of the same 

 plant, for he saw growing among them a nearly complete 

 series of intermediate forms. 



Hybrids. — ^Hybrids are neither species nor true varieties. 

 The hybrid being produced from a seed which is formed 

 by the co-operation of two parents, with certain distinct 

 characters, shares the characters of both, either latent or 

 expressed, or in an intermediate form. But the seeds of 

 hybrids do not breed true. Some of the descendants will 

 be hybrids like the immediate parents ; others may share 

 the hybrid characters in a different way ; while some will 

 always revert back to the pure form of the ancestral 

 types. 



The unit of classification must, then, be the distinct 

 race, which breeds true to seed. According to what we 

 have said, this, in general, will be the species ; but where 

 the species is subdivided into varieties which breed true 

 to seed, then these constant varieties will become the 

 units. De Vries gave the name " elementary species " to 

 varieties which breed true to seed. Inconstant variations 

 have no claim to varietal rank ; they are oaly of biological 

 interest, indicating the range of variation within the same 

 species. The characters of the true variety are permanent 

 and inherited. In horticulture new varieties are being 

 constantly produced. In one sense these are rarely new. 

 In flowers, most of them are hybrids. In this case man 

 assists Nature by bringing into breeding contact two 

 forms which are seldom or never found together. In 

 crops they are generally the isolated forms of already 



