THE AXGIOSPERMAE 1227 



separately into placentae, which may sometimes (Solanaceae, Scrophula- 

 riaceae) grow to occupy a large part of the loculus and bear very numerous 

 ovules. These placentae appear to arise from the central, fused tissues of 

 the ovar\', hence they are called axile. Only in a minority of cases is any 



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genuinely axial tissue included in the ovary axis. Some flower-rudiments 

 have a broad top to the receptacle, which is not all used up in carpel forma- 

 tion, and in such flowers the apex of the receptacle may rise between the 

 carpels and form part of the ovary axis. Examples are: Xymphaeaceae, 

 Alsineae (Caryophyllaceae), Ntgella, Oxalis, etc. The vascular bundles in 

 the recurved placental margins of the carpels show, as would be expected, 

 a reversed orientation, with the xylem outward. They are thus distinguish- 

 able even when they are embedded in the united tissues at the centre of the 

 ovary. Where the receptacle tissue forms a core, so to speak, in the ovary 

 axis, it may sometimes be distinguished by its vascular bundles with normal 

 orientation. This depends, however, on its extent, for the vasculation may 

 be reduced to a single concentric strand, or even be absent altogether when 

 there is little axial tissue. In the great majority of cases, therefore, the 

 placentation in truly syncarpous ovaries is based upon marginal placentation 

 in the individual carpels. The degree of union between the carpels varies 

 considerably. In many genera there is no actual fusion of tissues at the 

 centre and the placental margins of the carpels are free and easily recogni- 

 zable {e.g., Campanula, Erythraea), although the lateral walls are completely 

 united in the septa. 



The parietal position of the ovules in truly syncarpous, septate ovaries is 

 rare, just as the dorsal attachment of ovules in single carpels is rare. 

 Examples are found in the Aizoaceae and in Punka granatiim (Pomegranate) 

 but they are subject to doubt as possibly produced by secondary shifting 

 of the placentae. In Mesembryanthenum (Aizoaceae) the early stages of the 

 carpel show axile attachment of the ovules, which are apparently later 

 carried outwards and upwards on to the outer walls by intercalary growth. 

 Punica is also peculiar, for here there are two whorls of carpels, the inner 

 whorl of three having axile placentation, while the outer whorl of five, 

 which are eventually raised above the inner whorl by intercalar}^ growth, 

 has parietal placentation. 



Some examples of uniovulate loculi occur and it is commonly found 

 in such ovaries that the single ovule springs either from the base or 

 from the top of the ovar}^ axis. There is always the possibility in such cases 

 that we may have to do with ovules which are medianly placed on the sill 

 of a peltate carpel, rather than with the reduction of fertility in true marginal 

 placentae. There is, however, in some syncarpous ovaries a tendency for 

 one or more of such uniovulate loculi to become abortive, as we see in 

 Viburnum, J'a/en'anella and Stilbe, which may be looked upon as indicating 

 reduced fertility, at least in some cases. 



Parietal placentation on the septa, which appears to be quite distinct 

 from marginal placentation, occurs in Cytinus, a member of the Raftlesiaceae, 

 which is found in southern Europe. Numerous branching placentae are 



