388 SYSTEMATIC BOTANY. 



plants have originated, it is impossible to say with any certainty. 

 In the first case such races probably arose in an accidental 

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

 to produce certain variations or abnormal deviations from their 

 specific type, or to si^ort, as it is termed. By further cultivation 

 under the care of the gardener, such variations are after a time 

 rendered permanent, and can be propagated by seed. Such per- 

 manent 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 ; it will be seen therefore, 

 that races present well-marked characters by which they are 

 distinguished from true species. Hence, although our cereal 

 grains and culinary vegetables 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 observed, 

 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 hyhrldization. The varieties thus formed, which 

 are called hybrids or cross-breeds, are, however, rarely transmitted 

 by seed — although, in some instances, 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 ten- 

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

 be considered as permanent productions of Nature, which are 

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

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



* The above views as to the nature of species and varieties 

 are those which, until recently, have been almost universally en- 

 tertained by naturalists, but they are altogether opposed to those 

 that have of late years been 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," and in other 

 volumes. These authors contend, that species, so far from being 

 immutable, are liable to change of almost any extent, — in fact, 

 that plants, by the operation of causes acting over a long period 

 of time, may become so altered, that they preserve scarcely any 

 apparent resemblance to those from which they were originally 

 derived. At present, however, although fully admitting the very 

 great ability with which these opinions have been supported, 

 we must, until further evidence be adduced, adhere to the views 

 above expressed, as to the nature of species and varieties. 



