THE STUDY OP THE EVOLUTION OF THE FLOWEE. 297 



Vasculah STurcTURE OF THE Plower IN Angiosperms. — Since Van Tieghem's * 

 memoir of 1868, wlien the vascular systems of several evolutionary types of both mono- 

 cotyledonoiis and dicotyledonous flowers were examined, this subject has progressed very 

 little beyond the purely descriptive stage. Hence the leading features of economical 

 advance maybe outlined here. The simplest trace of a single carpel consists of a median 

 or dorsal and tw^o marginal or ventral bundles. In the Hellebore, where the carpels are 

 united at their bases, bivalent traces occur in the basal portion. Pronounced cases of 

 syncarpy reveal two series of bundles in the ovary- wall — the outer homologous with 

 dorsal, the inner wdth marginal bundles, and in GetYininm longipes the marginal 

 bundles coalesce in pairs. The vascular changes which supervene with perigyny and 

 epigyny vary in different families. In Aralia the stemonal and perianthic traces, now 

 included in the ovary-wall, form a third and outermost series of bundles. The two 

 outer series, distinct in Aralia, have become synthesized to form one in Castanea, several 

 genera of Cornace^, and the epigynous Sympetalse. The amalgamation is incomplete 

 in Davidia and Marlea. Another mode of origin of the single outer series is indicated 

 in the Hamamelidaceje, where the single series of bundles, evident as far as the insertion 

 of the perigyuous ridge, might have a further upward extension as the ovary becomes 



inferior. 



The last traces of the dorsal carpellary bundles may disappear, as in Lonicera and 



Leycesteria, but here the bundles passing to stamens and petals are perhaps not strictly 

 homologous with stemonal and petal traces respectively. 



By a further economical advance the bundles in the single series, which in Cornus, 

 Leycesteria, and many other genera are equal to the sum of the petals and stamens, are 

 in Viburnum, the Campanula ceae, and Compositse reduced to one-half the number. 



Lines of asymmetrical development are exemplified by Viburnum, a precursor of the 

 irregular vascular systems which prevail in the Valerianaceae. 



No phylogenetic significance can be attached to a particular form of vascular system ; 

 but vascular details may afford a clue in support of an interpretation of origin, as in 

 Viburnum, Aucuba, etc., but they should always be used with the utmost reserve. 



>> 



The Ovule in Angiosperms.— Mirbel f wrote in 1829 : " On peut dire qu a cette 

 premiere epoque tons les ovules sont orthotropes 



The orthotropous ovule is primitive to the anatropous types. 



The ovule, in Juglmis regia, according to Benson and WelsfordJ, is not strictly 

 orthotropous, but exhibits " one mode of the phylogenetic origin of the orthotropous 

 basal ovule from an anatropous parietal type." Benson and Welsford describe two 

 types of flower: in one there are two opposite basal parietal placentae, of which one b 

 a single erect ovule and the other is barren ; in the other, the ovule is apparently borne 

 by the two placenta? and becomes basal and orthotropous. Now, in the first case, the 



• Ph. Tan Tieghem in Ann. Sei. Nat., Bot. o'^" ser. ix. (1868) 127-226, t. 9-12. 

 t Mirbel in ilem. de I'Acad. des Sciences, ix. (1830) 611. 



Welsford 



2 X *> 



