EXOGENS. 2-1 J 



combinatioua can be eflected by such distinctions. Exceptions to the 

 constancy of such characters are endless ; there is probably not one polype- 

 talous Order that is not also apetalous, and many of them are even 

 monopetalous, of which Rueworts, Ilouseleeks, Anonads, Leguminous plants, 

 Milkworts, and many more, afford famihar examples. The apetalous Orders 

 are occasionally polypetalous, as in many genera of Buckwheats andDaphnads. 

 The monopetalous structure becomes polypetalous in all but a very few cases, 

 even indeed in such natural Orders as the Primworts ; and it even disappears 

 altogether, as in Oliveworts and Primworts. Nor is it probable that charac- 

 ters derived from the calyx and corolla should be of the very highest value ; 

 for, in the first place, those organs are physiologically identical, their 

 distinction having no real existence except in certain special instances ; 

 and, in the next place, the importance of them to the act of reproduction 

 can hardly be considerable, when we find that plants are multijilied quite as 

 well in their absence as in their presence, and even that, as in the Violet, 

 some Leguminous plants, the common Apple, (fee, which habitually produce 

 them, seeds are matured as freely when they are partially away as when in 

 a state of high development. For this reason, the calyx and corolla are 

 here rejected as organs suited for distinguishing the primary groups, or 

 the Sub-classes, of Exogens. 



We are not, however, justified in assuming that the calyx and corolla 

 are never of any high importance in plants ; and, therefore, while they 

 are objectionable as forming the basis of a classification per se, they are 

 recognised as having a real value in connection with the stamens. If the 

 stamens have no adhesion to either calyx or corolla, then it may be assumed 

 that the latter organs may be dispensed with ; and for this reason the first 

 Sub-class of hermaphrodite Exogens is characterised by the stamens standing 

 entirely clear of the floral envelopes, or being, in the language of Jussieu, 

 Hypogynous. But if there is any adhesion between the stamens and either the 

 calyx or corolla, it may equally be assumed that the one organ is in some way 

 necessary to the other ; for this reason the Perigynous character is admitted 

 as a valid mark of a Sub-class ; not, however, a slight and inappreciable 

 adhesion, but a real and manifest union of the parts ; and it is considered 

 immaterial whether the stamens grow on the petals or the calyx, provided 

 they grow on one of them. 



Beyond this we have that further degree of adhesion, to which Jussieu 

 gave the name of Epigynous : consisting of a union not only of the calyx or 

 corolla to the stamens, but of all those organs to the sides of the ovary. 

 This, in which it may be supposed that a higher degree of necessity for the 

 incorporation of the floral organs exists than in the former case, is taken as 

 the distinctive mark of a third Sub-class of hermaphrodite Exogens. So 

 that the Sub-classes are established on the following grounds : — 



Floivers absolutely unisexual I- Diclinous. 



Flowers hermaphrodite. 



Stamens not adhering to either calyx or corolla IL Hypogynous. 



Stamens adhering to either calyx or corolla Ill- Perigynous. 



Stamens, calyx, and corolla all adhering to the side of the ovary IV. Epigynous. 



This, it may be said, is essentially the old plan of Jussieu ; but there is 

 this material diff'erence between the method now proposed and that of the 

 great chief of the French school : that what he treated as a secondary 

 character is made primary ; while his primary distinction, of polypetalous, 



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