ANGIOSPERMS. 



5<^5 



surmount the ovary, which may therefore be considered to be composed of a single 

 carpel which rises up from the floral axis as an annular zone. In Piperacese 

 however the stigma, which is sessile on the apex of the ovary, is often placed 

 obliquely or divided into several lobes ; and this, like the two or four styles 

 which surmount the ovary of Naias^, indicates that the ovary is not composed of 

 one but of several carpels, which first make their appearance, like the leaf-sheaths 

 of Equiseium^ as an unbroken ring, which only at a later period becomes resolved 

 at its upper margin into teeth. This hypothesis appears the more admissible 

 since, in other Angiosperms where a comparison with nearly allied forms justifies 



Fig. 391. — Longitudinal section of the flower ol Rheiitn 

 undulatunt ; jleaf of the outer,/ of the inner perianth- whorl ; 

 a a a three of the nine anthers.y ovary, « stigma, ,t,4nucellus 

 of the ovary, dr glandular tissue at the base of the filaments 

 forming the nectaries. 



Fig. ■y)2.—AnagciUis arvenszs ; A longitudinal section of 

 a young flower-bud, / sepals, c corolla, a anthers ; A' carpel ; 

 S apex of the floral axis ; B the gynaeceum further developed, 

 the stigma « being now formed, and the ovules on the central 

 placenta 5 ; C the gynaeceum ready for fertilisation, / pollen- 

 grams on the stigma n,gr style, ^central placenta, 5"A'ovules; 

 D unripe fruit, the placenta 5 has become fleshy and swollen 

 so as to fill up the spaces between the ovules. 



US in inferring a number of coherent carpels, these carpels originate as an un* 

 divided annular zone which developes into the ovary, style, and stigma ; as, for 

 instance, in Primulaceae (Fig. 392) (free central placentation). In Polygonaceae, on 

 the other hand, where the ovary also forms eventually a closed cavity containing the 

 central ovule (Fig. 391), the cohesion of two or three carpels to form the ovary may 

 not only be recognised from the corresponding number of the styles and stigmas ; 

 but separate carpels appear at first distinct on the floral axis, and only amalgamate 

 in the course of their growth, their zone of insertion becoming elevated as a ring. 

 Since the wall of the ovary does not in any of these cases form placentae from 



^ I am unable to understand why Magnus calls the wall of the ovary 'perianth.' 



