SECTION 18.] KINDS AND RELATIONSHIP. 177 



utmost importance in cultivation and of considerable consequence in the 

 flora of any country, are of less botanical significance. For they are apt 

 to be indefinite and to shade off one form into another. But species, the 

 botanist expects to be distinct. Indeed, the practical difference to the 

 botanist between species and varieties is the definite limitation of the one 

 and the indefiniteness of the other. The botanist's determination is partly 

 a matter of observation, partly of judgment. 



526. In an enlarged view, varieties may be incipient species ; and nearly 

 related species probably came from a common stock in earlier times. For 

 there is every reason to believe that existing vegetation came from the 

 more or less changed vegetation of a preceding geological era. However 

 that may be, species are regarded as permanent and essentially unchanged 

 in their succession of individuals through the actual ages. 



527. There are, at nearly the lowest computation, as many as one hun- 

 dred thousand species of phanerogamous plants, and the cryptogamous 

 species are thought to be still more numerous. They are all connected by 

 resemblances or relationships, near and remote, which show that they are 

 all parts of one system, realizations in nature, as we may affirm, of the con- 

 ception of One Mind. As we survey them, they do not form a single and 

 connected chain, stretchiug from the lowest to the highest organized 

 species, although there obviously are lower and higher grades. But the 

 species throughout group themselves, as it were, into clusters or constel- 

 lations, and these into still more comprehensive clusters, and so on, with 

 gaps between. It is this clustering which is the ground of the recognition 

 of kinds of species, that is, of groups of species of successive grades or 

 degree of generality ; such as that of similar species into Genera, of genera 

 into Families or Orders, of orders into Classes. In classification the se- 

 quence, proceeding from higher or more general to lower or special, is always 

 CLASS, ORDER, GENUS, SPECIES, VARIETY (if need be). 



528. Genera (in the singular, Genus) are assemblages of closely related 

 species, in which the essential parts are all constructed on the same partic- 

 ular type or plan. White Oak, Red Oak, Scarlet Oak, Live Oak, etc., 

 are so many species of the Oak genus (Latin, Quercus). The Chestnuts 

 compose another genus; the Beeches another. The Apple, Pear, and 

 Crab are species of one genus, the Quince represents another, the various 

 species of Hawthorn a third. In the animal kingdom the common cat, the 

 wild-cat, the panther, the tiger, the leopard, and the lion are species of the 

 cat kind or genus ; while the dog, the jackal, the different species of wolf, 

 and the foxes, compose another genus. Some genera are represented by 

 a vast number of species, others by few, very many by only one known 

 species. For the genus may be as perfectly represented in one species as 

 in several, although, if this were the case throughout, genera and species 

 would of course be identical. The Beech genus- and the Chestnut genus 

 would be just as distinct from the Oak genus even if but one Beech and 

 one Chestnut WPJ-A Vnpwp ; as indeed was once the case. 



