THE STUDY OF THE EVOLUTION OF THE FLOWER. 281 



in Ilelwingia. Now Bentliam and Hooker state that the Cornacege and Araliacese are 

 to he distinguished by the type of ovule prevailing in the family ; so they were evidently 

 unaware that the ovule, in Helwingia^ does not conform to the Aralian type, with 

 ventral raphe, and hence could not belong to the latter family. If, then, the genera 

 are not closely related, the arguments bearing on the homology of the perianth diminisl 



1 



in value. 



Another solution of the puzzle presents itself, however. It will be observed that the 

 perianth leaves alternate with stamens in the male flower, corresponding in position to 

 petals; but in the female flower they alternate with the stisrmas, and might represent 

 sepals. Now if the perianths of the male and female flowers are homologous, it is 

 conceivable that some anomaly exists with regard to the stamens. If it were supposed 

 that the flower was primitively ob- or diplostenionous, but has lost the inner or outer 

 whorl of stamens, as the case may be, then the perianth segments could be interpreted 

 as sepals and the orientation of the whorls in both the male and female flowers could be 

 explained. Among Cornaceae a double whorl of stamens has been recorded in Nyssa 

 sessiliflora. 



Comparison between Ilelwingia and Cornus. 



Morren and Decaisne * established Helwingia in a new family, the Helwingiacese. 

 This arrangement was subsequently criticised by Baillonf, who states that Decaisne was 

 misled by artificial characters. Baillon points out that the female flower is constructed 

 very like the flower of CornuSy and the ovules of both genera are of the same type. He 

 considered that Bentham and Hooker, in placing Helwingia among the Araliaceae, were 

 led astray owing to the numerous agreements in character and organization between 



Hdwingia and Meryta. 



Now the ovules of Cornus (with dorsal raphe) are orientated tangentially — an orienta- 

 tion that appears to be constant for the Capri foliacese ; whereas those of Helwingia (with 

 dorsal raphe) are radially orientated, and the position taken up in the loculus seems to be 

 the outcome or result of a genetic difference in the ovule, as explained by the writer in 

 a previous paper. Hence the ovules of the two genera are not necessarily homologous, 



considered by Baillon 

 Ag^ain. the vascular s 



■ r 



ystems do not correspond. That of Helwingia, owing to the 



existence of separate perianth and dorsal carpellary bundles, agrees more nearly with 

 Aralian type. The vascular supply to the ovule is different in the two cases. In 

 helwingia each axial bundle divides to form three, of which the median enters the 

 ovule ; in Cornus, lateral branches from a pair of opposite peripheral bundles unite to 

 form the ovular trace. These details show that the resemblances between the two 

 genera are not so real as Baillon supposed, and that he himself was influenced 

 structural parallelisms. 



♦ ilorren et Decaisne in Bull. Acad. Brux. v. (1836) 169. 



t H. Baillon in Bull. Soc. Linn. Paria, i. (1877) 137. 



2t2 



