36 Mr. R. Brown on the relative position of 



equally ovuliferous, which is the case in a few families of very 

 small extent, as Butomece, Nymphaacece and Lardizabalece. 



Secondly. Where the production of ovula is limited to the 

 external angle of the cell or axis of the leaf supposed to form 

 the carpel. 



A case of this kind is found in a portion of one of those 

 families in which the whole surface is generally ovuliferous, 

 namely, in Hydropeltidece, which I have always regarded as 

 merely a section of Nymphceacede * ; and from the nature of 

 these differences in placentation, which are more apparent 

 than real, an argument might even be adduced in favour of 

 that opinion. 



A placenta apparently limited to the outer angle of the cell 

 also occurs in the greater number of species of Mesembry- 

 anthemum. As this structure, however, is certainly not with- 

 out exception in that very natural genus, several species, 

 among which are Mesembryanthemum crystallinum, cordi- 

 folium, papillosum and nodiflorum, having the placenta con- 

 fined to the internal angle of the cell or margins of the carpel ; 

 and as in some of those species in which the outer angle is 

 placentiferous, the production of ovula is not confined to it, 

 but extends to the lower half of the inner angle ; — this ap- 

 parent deviation from ordinary structure may perhaps be ex- 

 plained by assuming cohesion of the inflected portion of the 

 carpel with the wall of the cell ; — an hypothesis, in some 

 degree supported by the fact, that in several species the ter- 

 mination of the assumed inflected portion is free and not 

 ovuliferous. 



But whatever opinion may be adopted as to the relation of 

 this seemingly anomalous to the ordinary structure, it cannot, 

 as M. Fenzl proposes t* be employed as the essential cha- 

 racter of a distinct natural family limited to the Linnaean 

 genus Mesembryanthemum, 



The placenta then of a simple ovarium in its usual state, 

 according to this view, is necessarily double ; though by the 

 complete suppression of ovula in one of its two component 

 parts, and their diminished production in the other, the 

 ovarium is not unfrequently reduced to a single ovulum. 

 That such is the origin of the single ovulum is at least mani- 

 fest in a monstrosity of Tropaeolum majus, in which the stamina 

 are converted into pistilla ; but the complete action being im- 

 peded by the presence of the regular trilocular pistillum, and 

 the two marginal cords of each open ovarium remaining di- 



* Gen. Rem. in Flinders 's Voy. vol. ii. Append, p. 598. 

 f Annal. des Wien. Mus. vol. i. p. 349. 



