44 STTB-DIVISIONS OF EXOGENS. 



EXOGENS. 



Exogens comprehend by far the larger portion of flowering plants, 

 though several of the most important and extensive families belong to 

 the ranks of the Endogens. Every diversity of configuration occurs 

 among them, and every variety of size, from the groundsel up to the 

 oak-tree. There are scattered up and down their various tribes, root- 

 less plants, stemless plants, leafless plants, and in not a few there are 

 neither calyx nor corolla. The whole are susceptible, nevertheless, of 

 distribution into 



Plants with bisexual flowers, 

 and 



Plants with unisexual flowers. 



Bisexual Exogens. — While most flowering plants ai'e Exogens, most 

 of the latter are bisexual. How to separate these becomes the 

 next consideration, and a seriously important one, since the families 

 are very numerous ; while in regard to the grand preliminary groups 

 which imdoubtedly they are referable to. Nature has refused to dis- 

 close her plan with perspicuity. The beginning and the ending are 

 made plain, but the space lying between is half-hidden. One school 

 of botanists resolves them into such as possess both calyx and corolla, 

 or "Dichlamydeiti," and such as have calyx only, or " Monochla- 

 mydeaj," throwing the former into three sub -divisions, characterised 

 by the insertion of the stamens, whether on the receptacle, on the sepals, 

 or on the petals. The arrangement is meritorious, without doubt. It 

 appears, however, neither so natural nor so eligible as that which, 

 disregarding the uncertain distinction of presence or absence of corolla, 

 disposes the whole of the families simply and at once imder the three 

 following heads : — 



Flower enclosi7ig the ovary, both calyx and corolla being removable 

 without touching it ; the stamens growing upon the receptacle, 

 jyid thus as free and independent as the ovary. 

 Flower and ovary as in the first section, but the stamens attached 



either to the calyx or corolla. 

 Flower (including calyx, petals, and stamens) growing upon the 

 suDwiil of the ovary. Not that it is absolutely generated there, 

 but the lower portion intimately adherent to tlie sides of the 

 ovary, as explained on page 28.* 



• No special nutiios liavo bi'on given (o these tliree groups ; thej' are simply 

 called lljpogyuous Kxogens, rerigynous Exogeus, and Kpigynous Exogens. 



