396 SYSTEMATIC BOTANY, OR 



and may be illustrated by the different races of mankind now 

 existing in different parts of the earth, all of which have, as we 

 know, sprung from a single pair of individuals. How such 

 races of plants have originated, it is impossible to say with any 

 certainty. In the first case such races probably arose in an ac- 

 cidental manner, for it is found that plants under cultivation are 

 liable to produce certain variations or abnormal deviations from 

 their specific tyj^e, or to sport, as it is termed. By further cul- 

 tivation under the care of the gardener, such variations are after 

 a time rendered permanent, and can be propagated by seed. 

 Such permanent varieties however, if left to themselves, or if 

 sown in poor soil, will soon lose their peculiarities, and either 

 perish or return to their original specific type; such races there- 

 fore present well-marked characters by which they are distin- 

 guished from true species. Hence, although our cereal grains 

 and culinary vegetables, &c., have become permanent varieties 

 by ages of cultivation and by the skill of the cultivator, they 

 can only be made to continue in that state by a resort to the 

 same means, for if left to themselves they would, as just ob- 

 sers'ed, either perish or revert to their original specific type; 

 and hence we see also, how important is the assistance of the 

 agriculturist and gardener in perpetuating and improving such 

 variations. 



Another cause, which leads to constant variations from the 

 specific type, is hybridization. (See Hybridization.) The va- 

 rieties thus formed, which ai'C called hybrids or cross-breeds, arc 

 however, rai-ely transmitted by seed — although, in some in- 

 stances, such is the case for a few generations — but they 

 gradually revert to one or the other parent stock. 



We have now seen that species, under certain circumstances, are 

 liable to variations, but that all such varieties have a tendency 

 to revert to their original specific type. Hence species must be 

 considered as permanent productions of Nature, which are 

 capable of varying Avithin certain limits, but in no cases capable 

 of being altered so as to assume the characters of another species.* 



* The above viewsas to the nature of species and varieties 

 are those most commonly entertained by naturalists, but they 

 are altogether opposed to those recently brought forward by 

 Darwin and Wallace, and which have been fully and most ably 

 developed in a work by the former, " On the Origin of Species." 

 These authors contend, that species, so far from being immutable, 

 are liable to change of almost any extent, — in fact, that ])lants 

 by the operation of causes acting over a long period of time, 

 may l)ecomc so altered, that they prcseiwc scarcely any a])parcnt 

 resemblance to those from which they sprung. At present, 

 however, nhliougli fully admitting the very great ability with 

 nhicli these oi)inions have been su])i)orted, we must, until further 



