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ANALYTICAL CLASS-BOOK OF BOTANY. 



plants differing among themselves as much as these, or 

 even more. This, then, is the law in accordance with 

 which plants are distributed into species. Whatever 

 differences are merely accidental, produced by circum- 

 stances of climate or soil, and are not incompatible with 

 this principle, may, and do exist, between individuals of 

 the same species. Those differences, however, which are 

 incompatible with a common origin of the individuals 

 possessing them, become, in our observations, and in 

 botanical descriptions, the most valuable and certain 

 means of distinguishing between different species. Hence 

 we may regard our description of a species as that of a 

 type, or model, containing all those particulars in which 

 all the individuals comprehended under that species must 

 agree, and excluding all in which they may, and do differ. 



Those forms which exhibit those unessential differ- 

 ences in size, color of the flower, and general appearance, 

 produced by variations in climate, soil, or other acciden- 

 tal conditions, when they differ from the original type, 

 either considerably in some part of their structure, or in 

 general aspect and appearance, are termed VARIETIES. 

 These varieties are distinguished from species, which 

 preserve their peculiar characteristics under all circum- 

 stances, by their constant tendency to run into each 

 other, and to revert to their original type. Hence, 

 though we meet with varieties differing remarkably from 

 the primitive types, we usually find numberless interme- 

 diate varieties, forming by almost insensible gradations, 

 a complete and unbroken transition to the original char- 

 acter. The peculiarities of varieties, unlike those of 

 species, are rarely transmitted, unchanged, through the 

 seed ; but plants grown from the seed of a single indi- 

 vidual often present remarkable diversities. This is due 

 principally to the unstable character of these peculi- 

 arities, but also to another fact, which forms the most 

 certain and reliable test, to enable us to distinguish be- 

 tween what are really different species and what are 

 merely different varieties of the same species. Varieties 

 freely hybridize with each other, that is, the pollen of 

 one variety, brought by winds, or by insects, often fer- 

 tilizes the ovules of another ; the resulting plant com- 

 bines the peculiarities of both varieties, and is a hybrid, 

 or intermediate variety. These hybrids, between dif- 

 ferent varieties of the same species, it must be noticed, 

 produce seeds which are as perfect and as productive as 

 any. This property the horticulturist often avails him- 

 self of, in raising new varieties of fruits or flowers, by 

 combining in this way the merits of two previously ex- 

 isting varieties. 



But if we undertake to compel really different species 



to hybridize, the result is different. Either the pollen 

 refuses to fertilize the ovules at all, and no seeds are 

 produced, or if perfect seeds are produced, the plants 

 grown from them either refuse to produce perfect seeds 

 at all, or will do so only when impregnated with the pol- 

 len of one of the original species. Hence we see that no 

 permanent hybrid, or variety, can be produced between 

 two really distinct species. Any such forms, which may 

 accidentally be produced, either die out without leaving 

 behind them any progeny, or, in the course of a few 

 generations, revert back completely to one of the original 

 species. It is probable that if any really permanent 

 hybrids have ever originated between two apparently 

 distinct species, that these supposed species must have 

 been really very distinct varieties of the same species 

 which, under some accidental concurrence of circum- 

 stances and conditions, had retained so long their pecu- 

 liarities, that these differences have assumed an unusual 

 permanence, so as to be transmitted through the seed 

 nearly or quite unchanged. 



Such permanent varieties, when their characteristics 

 are perpetuated through the seed, though quite rare 

 among wild plants, are very common among those that 

 are cultivated. These varieties are often called RACES. 

 They probably arise much in the manner described 

 above, and are usually most permanent in those plants 

 which have been cultivated longest. Different countries, 

 or different districts, usually cultivate different varieties, 

 which have arisen under the influence of their climate, 

 soil, and other peculiarities of situation. These varie- 

 ties, however distinct from each other, or from the origi- 

 nal type in their general appearance, hybridize freely 

 with each other, and thus reveal their common origin 

 and specific unity, as they also do by their tendency, 

 when neglected, to revert to their primitive forms. 



As a species consists of individuals formed after the 

 same model, so a GENUS is a group of allied species 

 formed after the same general type, or model, and 

 more closely related to each other than to any other 

 species. The differences between such species, though 

 constant, are generally so few, and the plants usually 

 bear so close a general resemblance to each other, that 

 all, even the most ignorant, acknowledge their affinity by 

 bestowing upon the whole group one general name. Thus 

 the numerous species of the genus Rosa have always been 

 known under the common name of Rose, while the par- 

 ticular species have been designated by some adjective, 

 as the White, Red, or Damask Rose. So also in the 

 numerous species of Oak, the family resemblance has 

 always been recognized by the comprehensive name 



