240 EXOGENS. 



modifications which are found in the organs of reproduction may be expected 

 to furnish the best characters for classification, after those of nutrition. 

 The latter have been already employed as the foundations of the classes, as 

 far as they appear susceptible of being so applied ; the former, consisting 

 of the stamens and pistil, have been little used for the classes, and 

 appear to present as many modifications as are required for secondary 

 divisions. That was the opinion of Linnaeus, who adopted them in the 

 construction of the Classes and Orders of his sexual system ; but he mainly 

 relied upon their number, which is a circumstance of little or no importance, 

 and where that was done his classification proved useless ; but in those 

 parts of the system in which he made use of other circumstances, as in his 

 Monadelphia, Diadelphia, Tetradynamia, Didynamia, Syngenesia, &c., his 

 divisions ceased wholly or in part to be artificial, and although in some 

 instances modified, still correspond essentially with the Natural Orders of 

 modern botanists. 



Nor did the importance of the stamens and pistil escape the keen eye of 

 Jussieu, who relied upon them very much in the construction of his inge- 

 nious system. In the first place, he separated from all other Exogens 

 those which have the stamens in one flower and the pistil in another, and 

 he called them Diclinous, and by this process he brought together a collec- 

 tion of Natm-al Orders, corresponding with the Monoecious and Dioecious 

 plants of Linnaeus. No one can doubt that this was a judicious step, and 

 upon the whole the plants collected in the diclinous division resemble each 

 other more than they resemble anything else ; but he excluded a large 

 number of truly diclinous plants, which are scattered over other parts of 

 his classification, and this has led to the idea that the distinction itself 

 was a bad one, an opinion in which I formerly concurred ; but a more 

 careful examination of it since, and an extended acquaintance with the 

 Vegetable Kingdom, has entirely convinced me that we have no available 

 characters for breaking up Exogens into primary groups or sub-classes 

 superior to those of separated and united sexes, that is, to diclinism and 

 hermaphroditism. Not that they are without exceptions ; to employ the 

 forcible language of Jussieu himself: " Ut vi prcecedenti serie nonnullas 

 didinis hermaphroditis commixtas plantis admittit exceptio, sic in didinium 

 07'dines qucedam irrepunt hermaphroditce, consentienie aut jubeiite naturd 

 qucB stabiliores interdiim eludit regidas, nonnunquam instabilis ipsa aut 

 abstrusis legibus obtemperans.'' — Gen. PL 384. But if what are called 

 polygamous plants, that is to say, such as have a rudimentary pistil in the 

 male flowers, and rudimentary stamens in the female flowers, are regarded 

 as being hermaphrodite, as they surely are, and the idea of a diclinous 

 structure is limited to cases of a total separation of the stamens and pistil, 

 these exceptions are reduced to a small and unimportant number, of no 

 moment in a classification. For this reason, then, the diclinous sub- 

 class of Jussieu is still preserved ; increased by modern discoveries and 

 improved by the expulsion of such plants as Piper, Gnetum, Ulmus, and 

 others which belong to hermaphrodite Orders, or have other affinities than 

 those suggested by Jussieu. 



In this way Exogens are broken up into 2 groups, the one Diclinous and 

 the other Hermaphrodite. The latter is divided by almost everybody 

 into Polypetalous, Monopetalous, and Apetalous sub-classes ; following the 

 old systematists, who knew of little beyond external characters, and had 

 small acquaintance with any plants except those of Europe. But all 

 experience shows, what reason seems to indicate, that no great natural 



