STRUCTURE.] MARGINAL PLACENTATIOST POSSIBLE. 



shows, which represents the real leaf. The supposition that 

 the ovule originates from the midrib of a metamorphosed 

 leaf i far more natural, and explains better the forms of the 

 pericarp, if we only admit the inflection and slight coherence 

 of the margins/' 



But it does not follow that, because the placenta has some- 

 times, it must always have, such an origin. We know that 

 leaves do produce buds, we also know that the axis produces 

 them ; there is, therefore, no reason why the carpels, as well 

 as the point of the axis which they enclose or surround, 

 should not in like manner produce ovules. In fact, we have 

 numerous cases of monsters, especially in Houseleeks (Cras- 

 sulacese) and Crowfoots (Ranunculacese), in which the ovules 

 do most certainly grow on the margins of leaves only partially 

 converted into carpels. (See a remarkable example in Ele- 

 ments of Botany, p. 88. fig. 180.) Moreover, Dr. Grisebach, 

 in his excellent Genera et Species Gentianearum, has shown 

 that the placenta of that order cannot be an expansion of the 

 axis, because the ovules are originally developed in two or 

 three rows on the face of the carpels, forming a line of 

 minute tumours from the base to half-way up the carpels ; 

 " quae quidem series, parenchymate magis inter ovula quam 

 in dorso carpophylli crescente, demum ipsius superficiem fere 

 integram subaequaliter obtegunt." 



The placentation of Water-lilies (Nymphaeaceae), Broom- 

 rapes (Orobanchaceae), and Butomads, is equally at variance 

 with the central theory ; and, in their valuable paper upon 

 the successive formation of the parts constituting the fructi- 

 fication of Leguminous plants, Schleiden and Vogel have 

 clearly shown that in that case the carpellary leaf is originally 

 a folded scale, and that when the ovules appear it is from the 

 margins of that leaf, and not from the central point of the 

 axis. (Beitrdge zur Entwickelungs-geschichte der Bluthentheile 

 bei den Leguminosen.} 



The preceding theoretical views would seem to be in all 

 respects satisfactory. It is, however, necessary to add that 

 Dr. Robert Brown thinks that perhaps the structure both 

 of ovary and anthers is not obviously reconcilable to any 

 hypothesis hitherto proposed to account either for the origin 



