21G SCIENCE OF THE STUDY OF TREES. I'AUT II. 



pnal species ; because a tendency to this has been found to take place both in 

 plants and animals. 



Varieties. — A variety diflcis from a race, in not being susceptible of propa- 

 gation by seed, at least witli any thing like constancy and certainty. For ex- 

 ample, the jargonelle pear maybe continued by seed ; but a jargonelle pear 

 with varit'gatod foliage could not be so propagated with certainty. We allow, 

 however, that, if a great many seeds taken from the fruit of a jargonelle pear 

 with variegated leaves were sown, some of tiie plants so raised woidd pro- 

 bably siiow variegation in their foliage. The same thing, we think, would take 

 place in the case of sowing the seed of variegated hollies, or of fastigiate or 

 pendulous-branched plants, but to what e.\tent it is impossible to say. It 

 certainly would not take place to such an extent as to confound varieties with 

 races, or to render it desirable to propagate varieties in this way ; and, conse- 

 quently, \aricties are always pro[)agated by some modification of division, such 

 as by cuttings, layers, grafting, &c. 



Varialions differ from varieties in not being transmittible by any mode of 

 propagation. They are always produced by local circumstances operating on 

 the individual ; and the moment these circumstances are changed, the varia- 

 tion disappears. For example, plants grown in the dark will have their leaves 

 white ; other plants with hairy leaves, when grown in water, will have their 

 leaves smooth ; and the hydrangea, grown in a certain description of soil, will 

 have its flowers blue : but, remove the plant with white leaves to the light, 

 and place the plant grown in water in dry soil, and the hyilrangea in connnon 

 soil, and it will be found that the leaves of tlie first will become green, and 

 those of the second hairy, and that the flowers of the h3drangea will resume 

 their natural pinkish hue. 



Mules and Hybrids. — Some confusion exists as to the use of these terms, 

 when a[)plied to plants. The term mule, we think, ought to be limited to such 

 hybriils as are raised between different aboriginal species, and which it is be- 

 lieved are not susceptible of propagation by seed : such, for example, as the 

 i^yrus spuria, which seems to be a hybrid between Pyrns iSorbus or ^l^ria and 

 Pyrus Chama2mespilus. The term hybrid, on the other hand, we think, ought 

 to be limited to the produce, by cross fecundation, of different races and varie- 

 ties of the same species. Every one knows that this is one of the most im- 

 portant elements of culture, having given rise to the most valuable garden 

 flowers, table fruits, culinary vegetables, and agricultural plants. 



Botanical Species. — It will be seen, from the preceding remarks, that we 

 follow De CandoUe in denominating what Dr. Lindley and other British bo- 

 tanists distinguish as botanical species, races, or varieties. 



It is not to be supposed, however, that we undervalue botanical species, or 

 that we either deny the distinctness of many that exist, or the propriety of 

 having different names for them, and keeping them distinct. On the con- 

 trary, to conipare plants with men, we consider aboriginal species as mere 

 savages, and botanical species, or, according to De CandoUe's classification, 

 races and varieties, as civilised beings. What, then, it may be asked, is our 

 object in endeavouring to show that many of our botanical species are only 

 varieties ? We have two objects in view ; and both, we think, are very im- 

 portant ones. In the first place, by confounding varieties or garden or bota- 

 nical species with aboriginal ones, a beginner, ignorant of the extent to which 

 this is done, cannot make a judicious selection; and while, in the case i'mxi- 

 nus, for instance (of which there are, in reality, as we think, only three spe- 

 cies known, exclusive of (/rnus), if he wished to select, perhaps, three sorts, 

 lie nught, instead of selecting the three really distinct species, which would 

 give him a complete idea of the genus, fix on three of the varieties of F. ame- 

 ricana or of F. excelsior, which woidd only give him an idea of one species. 

 In the second place, we wish to ()revent beginners, in the study or cultivation 

 of trees, from puzzling themselves unnecessarily to make out the minute dif- 

 ferences which distinguish what are calleil botanical species; beheving, as we 

 do, that it is impossible to make out many of these from the specific charac- 



