EXOGENS. 247 



Sub-Class I. DICLINOUS EXOGENS. 



The plants thus named never, or at least very rarely, have bisexual 

 flowers, but consist of species in which the stamens constantly appear in 

 one kind of flower, and the pistil in another. They appear to constitute the 

 nearest approach that can be found to Gymnosperms, to which the whole 

 Amental Alliance might in fact be referred, if the carpels would open and 

 present the ovules naked to the action of the pollen. It is indeed impossible 

 to overlook, on the one hand, the close resemblance which exists between the 

 cones of an Abies among Conifers, and the female catkins of a Betula in 

 the Order of Birchworts ; or, on the other, the vegetation of a Coniferous 

 Ephedra, and an Amental Casuarina. 



These and similar Orders must be regarded as the simplest forms of 

 structure which Dichnous Exogens present, their condition reaching its lowest 

 state in Hornworts(Ceratophyllacea3). At this part of the Sub-class we have 

 so entire a transition to the Chenopodal Alliance by means of certain 

 Diclinous Chenopods, which form an exception to the general condition of 

 their Order, as to make it clear that the Hypogynous Sub-class stands parallel 

 Avith the unisexual Orders. 



If we advance along the line of Diclinous Alliances, towards those forms 

 whose organisation is the highest, such as Menispermads, Cucurbits, and 

 Papayals, we shall find that all the others have also lateral aflinities of a not 

 less manifest description. Thus Spurges, Juglands, and Papayals pass into 

 the Perigynous Rhamnads, Anacards, and Passion-flowers ; Spurges and 

 Nutmegs stand on the limits of the Hypogynous Byttneriads and Anonads ; 

 while the Epigynous Sandalwoi-ts and Loasads are closely approached by 

 the Diclinous Helwingiads and Cucurbits. 



These facts show, that, although in one direction such a series of affinities 

 may be perceived, as that of which use has here been made, yet that it must 

 be considered to be a very imperfect expression of the relationship borne 

 by the Dichnous to the bisexual Alliances and Orders. 



It woidd be possible to break up the Diclinous AUiances into Hypogynous, 

 Perigynous, and Epigynous clusters ; and to some it may appear that 

 such a distribution would have been more logical than what is now pro- 

 posed ; and perhaj^s that view is correct. But, upon the whole, it is doubtful 

 whether the advantages of that plan would have been equal to some of its 

 disadvantages. 



