176 CLASSIFICATION. [SECTION 18. 



524. Varieties. The White Oak, for example, presents two or three 

 varieties in the shape of the leaves, although they may be all alike upon 

 each particular tree. The question often arises, and it is often hard to 

 answer, whether the difference in a particular case is that of a variety, or 

 is specific. If the former, it may commonly be proved by finding such 

 intermediate degrees of difference in various individuals as to show that 

 no clear distinction can be drawn between them ; or else by observing the 

 variety to vary back again in some of its offspring. The sorts of Apples, 

 Pears, Potatoes, and the like, show that differences which are permanent 

 in the individual, and continue unchanged through a long series of gen- 

 erations when propagated by division (as by offsets, cuttings, grafts, 

 bulbs, tubers, etc.), are not likely to be reproduced by seed. Still they 

 sometimes are so, and perhaps always tend in that direction. For the 

 fundamental law in organic nature is that offspring shall be like parent. 



Races are such strongly marked varieties, capable of coming true to 

 seed. The different sorts of Wheat, Maize, Peas, Radishes, etc., are 

 familiar examples. By selecting those individuals of a species which have 

 developed or inherited any desirable peculiarity, keeping them from min- 

 gling with their less promising brethren, and selecting again the most 

 promising plants raised from their seeds, the cultivator may in a few 

 generations render almost any variety transmissible by seed, so long as it is 

 cared for and kept apart. In fact, this is the way the cultivated domesti- 

 cated races, so useful to man, have been fixed and preserved. Races, in 

 fact, can hardly, if at all, be said to exist independently of man. But 

 man does not really produce them. Such peculiarities — often surprising 

 enough — now and then originate, we know not how (the plant sports, as 

 the gardeners say) ; they are only preserved, propagated, and generally 

 further developed, by the cultivator's skilful care. If left alone, they are 

 likely to dwindle and perish, or else revert to the original form of the 

 species. Vegetable races are commonly annuals, which can be kept up 

 only by seed, or herbs of which a succession of generations can be had 

 every year or two, and so the education by selection be completed without 

 great lapse of time. But all fruit-trees could probably be fixed into races 

 in an equal number of generations. 



Bud-varieties are those which spring from buds instead of seed. 

 They are uncommon to any marked extent. They are sometimes called 

 Sports, but this name is equally applied to variations among seedlings. 



Cross-breeds, strictly so-called, are the variations which come from 

 cross-fertilizing one variety of a species with another. 



Hybrids are the varieties, if they may be so called, which come from 

 the crossing of species (331). Only nearly related species can be hybridized; 

 and the resulting progeny is usually self-sterile, but not always. Hybrid 

 plants, however, may often be fertilized and made prolific by the pollen 

 of one or the other parent. This produces another kind of cross-breeds. 



525. Species are the units in classification. Varieties, although of 



