DEFINITION OF SPECIES AND SUB-SPECIES. 409 



Sub-species are forms more widely difierent from recognised species 

 than varieties usually are, distinguished by -well-marked characters 

 affecting several organs, and occupying a definite geographical area, 

 but which probably spring from other and more widely diffused species. 

 Ball gives Euphrasia officinalis, and all its varieties, as an example of 

 a species ; while the small alpine yeUow-flowered Euphrasia minima is 

 considered by him as a sub-species. 



Dr. BosweU Syme, in his preface to English Botany, remarks, — 

 "It is often extremely difiScult to decide whether a certain form ought 

 to be regarded as a species or a sub-species. Occasionally, in a work 

 on descpptive botany, what are admitted as true species wiU be found 

 to be quite as closely allied to each other as two other forms which 

 the same author regards as mere varieties, or it may be as sub-species. 

 In fact, all botanists are guided in this matter by an imperfect kind 

 of judgment, which is sometimes not far removed from caprice." He 

 recognises as sub-species those plants which have less strongly-marked 

 differences between them than are found between generally received 

 species, but which are nevertheless too constant in their characters 

 to be considered mere varieties. 



The term variety is applied by him to forms which are, or are 

 supposed to be, confined to individuals, and which may revert to the 

 original tjrpe in a single or a few generations ; while a sub-species 

 transmits its peculiarities for an indefioaite period. Many mistakes, no 

 doubt, occur respecting variety and sub-species, which better observa- 

 tion and long-continued cultivation may in time meet. " A state " is 

 even less permanent than a variety, for it may be removed in the 

 same individual by altering the external circumstances, such as soil, 

 climate, place of growth, etc. , 



By scattering the poUen of one plant on the pistU of an allied 

 species, seeds are formed, which, when sown, produce intermediate 

 forms or hybrids (p. 297). Hybrids, however, are rarely perpetuated 

 by seed. While many hybrids are produced artificially, some are 

 also produced naturally. In giving names to hybrids, those of the 

 two parent species are often given. Thus, a hybrid between Ver- 

 bascum nigrum and Verbascum Lychnitis ' is called Verbascum nigro- 

 Lychnitis. In the case of the genus Ehododendron many hybrid forms 

 have been produced by applying the pollen of the Ehododendron 

 arboreum to the pistil of other more hardy species, such as K. ponticum, 

 E. caucasicum, E. catawbiense, and these are indicated by such names 

 as E. arboreo-ponticum, etc. Gardeners very often give special names to 

 these hybrids, and thus confusion is introduced into nomenclature. 

 For instance, Ehododendron arboreo-caucasicum has been called E. 

 Nobleanum, and Ehododendron arboreo-catawbiense has received the 

 names of E. altarclerense and E. EusseUianum, etc. Sometimes hybrids 

 are produced between species of different genera, as between Ehodo- 



