GENEEAL PRINCIPLES OF CLASSIFICATION 3 



nent ; for the successive generations which will be produced 

 will have a tendency to revert to the original species from 

 which such varieties have been obtained, so that the nature 

 of the plant raised will depend upon the character of the soil 

 in which it is placed, and the other external conditions to 

 which it is exposed. Thus, if we sow the seeds of a num- 

 ber of different varieties of Aj)ples, the fruit subsequently 

 produced by the new generation of Apple trees will, instead of 

 resembling that of their parents, have a tendency to revert to 

 that of the common Crab, from which species all such varieties 

 have been originally derived. Hence a variety differs essen- 

 tially from a species in the fact that it cannot be propagated 

 without tending to revert to the type from which it sprang. 



b. Baces. — Besides the varieties just alluded to, there are 

 others, which are called permanent varieties or races, because 

 their pecuHarities can be transmitted by seed. Familiar ex- 

 amples of such races are afforded by our Cereal grains, as Wheat, 

 Oats, and Barley ; and also by our culinary vegetables, as Peas, 

 Lettuces, Eadishes, Cabbages, Cauliflowers, and Broccoli. How 

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

 any certainty. At the outset they probably arose in an ac- 

 cidental manner, for it is fomid that plants under cultivation 

 are liable to produce certain variations or abnormal deviations 

 from their specific type, or to sport, as it is termed. By fiu'ther 

 cultivation under the care of the gardener, such variations are 

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

 These so-called permanent varieties, however, if left to them- 

 selves, 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 contuiue 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 origi- 

 nal 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 hybridisation. The varieties thus formed, which 

 are called hybrids and cross-breeds, are, however, rarely constant 

 for long— although, in some instances, such is the case for a few 



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