250 NATURAL mSTORY OF PLANTS. 



way ossentiiilly natural, tlie establishment of a group Milinsea, 

 where the outer petals are, as we have seen, far more similar to 

 sepals than to the pieces of the inner corolla. AVe knew in fact 

 that there were genera foreign to this group, such as Popoioia, 

 Mitri'p/iora, and Oropluea, in certain species of which the outer 

 petals were already becoming in form and size less like the inner 

 ])etals, and so were tending to approach the calycine leaves. 



3. The absence of the inner petals is of itself insufficient to cha- 

 racterize a genus, for there are genera, recognised as perfectly 

 natural, where the outer petals gradually become much smaller 

 than the inner ones, and before finally disappearing are even reduced 

 to very small spoon-like bodies. We may cite certain species of 

 Anona, Bollinia, and one abnormal BoUinia of the section Clathro- 

 spcnnuDi. Most species of Unona have a well-developed corolla ; but 

 in some it is quite absent. 



4. The independence or union of the pieces of the perianth has 

 never appeared to us sufficient to characterize a genus. Heccalohus 

 for instance is not merely Unona with a gamopetalous corolla ; other 

 features mark it out, and we liave sketched them.' But it is 

 impossible to make a generic distinction between those species of 

 Uvaria, Unona, and RoIIinia, in which the corolla comes off in a single 

 piece, and those other species of these genera whose structure is 

 otherwise quite the same." The corollas of the Monodoras, varying 

 ,iireatly in form, are all gamopetalous ; but this feature alone would 

 not be thought worthy to put them in a group apart^ if the peculiar 

 organization of their gynseceum did not give them so marked a dis- 

 tinction.^ Nor is the union or freedom of the calyx-leaves a cha- 

 racter of more value ; for it may happen that of two species of the 

 same genus, as closely allied as possible, the one may have free 

 sepals, the other an urceolate cal3'^x, with three teeth hardly pro- 

 jecting on the edge. 



5. The number and arrano^ement of the stamens. — We have 



• See p. 226. It might not, liowever, lie ini- eluded in Trigyneia by Bentham & Hookee, 



possible to meet with some species whieh should though its corolla is decidedly gamopetalous. 



connect this peims with one of the sections of ^ We should further notice the consequence 



Artabotrys. For the jircscnt the union of the of gamopetaly in this genus; it is that the three 



petals is at once sufficient to distinguish the divisions of the corolla superposed to the sepals 



genera. may finally appear to stand on the same verticil 



' It is no doubt for the same reascn that Hexa- as "the three outer ones. Probably this is not 



lobus branUiensU A. S. II. & Tul. has been in- the case when they are young. 



