496 PHANEROGAMS. 



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 forms placentae from the number and 

 position of which the number and position of the carpels might otherwise be more 

 easily determined, we are thrown back on the direct observation of the first stages 

 of development and on the numbers of the styles and stigmas. Failing this, the 

 solution of the question depends on morphological relationships which are still by 

 no means made out with sufficient certainty, notwithstanding the numerous re- 

 searches which have been made on the development of the flower. 



Fig. 361. — Longitudina section of the flower oi Rheion 

 jiticiitiatiim : s leaf of the outer, / of the inner perianth- 

 whorl : aaa three of the nine anthers, y ovary, 7t stig-ma, 

 kk nucleus of the ovary, dr glandular tissue at the base 

 of the filaments forming the nectaries. 



Vie -^60.— A naga/lis aj-venszs : A longitudinal section of 

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

 -S apex of the floral axis ; R the gynseceum further developed, 

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

 placental; Cthe gyna?ceum ready for fertilisation,/ pollen- 

 grains on the stigma «, i:r style, 5 central placenta, SK 

 ovules ; D unripe fruit, the placenta .S has become fleshy 

 and swollen so as to fill up the spaces between the ovules. 



Besides the number of the carpels which have coalesced to form the ovary, it 

 is a question of interest whether in any particular case the ovules have been pro- 

 duced laterally on the floral axis or as its terminal structure. In the cases of 

 Piperaceae, Polygonaceae, Naias, Typha, &c., where only a single ovule springs from 

 the base of the ovary, it is evident that this must be the terminal structure of 

 the floral axis ; and the investigations of Hanstein and Schmitz, Magnus, Rohrbach, 

 and Payer, have proved in addition that not only the ovule as a whole, but the 

 nucleus itself, must be considered as a terminal structure. It must not, however, 

 be inferred from this that every ovule which springs from the base of the cavity of 

 the ovary necessarily forms the apex of the floral axis ; for it is conceivable that the 

 axis itself may have ceased to grow, but has produced an ovule at the side of its 

 apex, a case which we shall meet with further on in the infeiior ovary of Compositae. 



