THE MORPHOLOGY ОЕ THE РЕТМОТАСЕХ. 293 
recorded by Marchand and others. Baillon * even mentions a species of Lysimachia in 
which the placenta was prolonged beyond the ovary in the form of a shoot bearing 
leaves, and which was cut off and struck as a cutting. 
Alphonse de Candolle and many others have noticed the placenta giving off leaves 
instead of ovules. : 
In double Primroses it is not unusual to find the placenta bearing ovules at its lower 
part and one or more carpels above (Pl. XL. figs. 12-15)—a condition which has its 
parallel in the singular instance described by Mr. Berkeley in a species of Dianthus +. 
Such instances as those just alluded to support the view that the placenta is an axial 
structure; nor is that notion necessarily invalidated by the very common occurrence 
of free central, marginal, and parietal placentation, with every intermediate state, in the 
ovaries of double Primroses; for the presence of ovules, as of buds, is of itself no proof 
either of the foliar or of the axial structure of the organ from which they spring. 
There are, however, many valid reasons for supposiug the placenta to be of foliar 
origin : thus Van Tieghem 1, who at one time considered the placenta of Primulacez to 
be the direct prolongation of the axis (Ann. Sc. Nat. 5* sér. 1868, t. ix. p. 211), is now 
satisfied that the vascular bundles of the placenta have their spiral vessels on the outer 
side, and that they are therefore appendicular. Оп the other hand, he admits that in 
_ cases of virescence or prolification, the axial system of the pedicel is abnormally pro- 
longed into the cavity of the carpels. In this latter case the trachee are internal. The 
vascular bundles of the placenta then, instead of being independent of the carpels, are 
offshoots from them. А similar conclusion is arrived at with reference to Theophrasia. 
Ina note appended to p. 622 of his translation of Sachs's * Lehrbuch,’ M. Van Tieghem 
gives the following summary of his present views, which it is convenient to cite in 
this place. 
* L'étude anatomique démontre que le pétale et l'étamine superposés (Primulaceze), 
пе sont que les deux parties d'une seule еб méme feuille ramifiée, qui а subi une méta- 
morphose héterogéne et double appropriée à deux fonctions différentes. Mais, en outre, 
elle fait voir que la colonne placentaire est formée, non par le prolongement de l'axe 
floral au dessus de l'insertion des carpelles, comme on l'admet généralement, mais par 
des dépendances liguliformes des carpelles qui constituent la paroi de lovaire unies et 
soudées entre elles dans l'axe géométrique de la fleur comme les сагреПев le sont eux- 
mémes latéralement dans toute leur étendue. De sorte que les ovules sont ici, aussi, 
insérés en définitive sur la feuille carpellaire, et qu'ils ont par conséquent la valeur 
morphologique de lobes de feuille "$. 
AL Braun || held somewhat similar views to Van Tieghem’s, and pointed out that many 
сазез in which the placenta appears to be axial may be explained by the congenital 
detachment of the bases of the carpellary margins and their fusion one with another 
ж Baillon, * Adansonia,’ iii. p. 310. + Gard. Chron. Sept. 1850, p. 612, and Veg. Terat. р. 268. 
+ Ann. Se. Nat. 5° sér. t. xii. p. 329 (1871); ‘ Recherches sur la structure du pistil’ etc. p. 91. 
$ Tréeul, however (Comptes Rendus, Oct. 23, 1876), contests Van Tieghem's views, and shows that in Anagullis 
the vessels of the placenta originate independently of and before those of the walls of the ovary. The parietal and 
placental vessels do not correspond in number ; nor are they continuous with, but quite free from, those of the thalamus. 
|| Analysis in Bull. Soc. Bot. France, Rev. Bibl. (1875) t. xxii. p. 63. 
SECOND SERIES.—BOTANY, VOL. 1. 2T 
