216 



SCIEiNCE OF THE STUDY OF TREES. 



PART IT. 



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

 plants and animals. 



Varieties, — A variety differs from a race, \t\ not being susceptible of propa- 

 gation by seed, at least with any thing like cohstancy and certainty. For ex- 

 ample, the jargonelle pear maybe continued by seedj but a jargonelle pear 

 with variegated foliage could not be so propagated with certainty. We allow, 

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

 with variegated leaves were sown, some of the plants so raised would pro- 

 bably show variegation in tlieir 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 extent 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, con- 

 sequently, varieties are always propagated by some modification of division, 

 such as by cuttings, layers, grafting, &c. 



Variations 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 hydrangea in common 

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

 of the second hairy, and that the flowers of the hydrangea will resume their 

 natural pinkish hue. 



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

 when applied to plants. The term mule, we think, ought to be limited to such 

 hybrids as are raised between different aboriginal species, and which, it isbe- 

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

 Pjrus spuria, which seems to be a hybrid between Pyrus iSorbus or J^ria, and 

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

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

 of the same species. Every one knows that this is one of the most important 

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

 table fruits, culinary vegetables, and agricultm^al 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. Un the con- 

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

 savages, and botanical si^ecies, 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 hnportant ones. In the first place, by confounding varieties or 

 garden or botanical 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 of Fraxinus, for instance (of which there are, in re- 

 ality, as we think, only three species known, exclusive of O'rnus), if he 

 wished to select, perhaps, three sorts, he might, 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. americana, or of F. excel- 

 sior, which would only give him an idea of one species. Jn the second 

 place, we wish to prevent beginners, in the study or cultivation of trees, 

 from puzzling themselves unnecessarily to make out the minute differences 

 which distinguish what are called botanical species; believing, as we do, 



