40 JOURNAT. OF THE ROYAL HORTICULTURAL SOCIETY. 



A PROBABLE ORIGIN OF EXISTING FLOWERS. 

 By Rev. Professor G. Henslow, M.A., F.L.S., V.M.H. 



[Read April 21, 1914 ; Mr. Joseph Cheal in the Chair.] 



Flowering plants are now grouped under two classes — Gymnosperms 

 and Angiosperms ; while the latter has two divisions — Dicotyledons 

 and Monocotyledons. 



There is no doubt that angiospermous Dicotyledons were evolved 

 from some, at present, unknown member or members of the gymno- 

 spermous plants of past geological ages ; while it has been proved by 

 experiments and induction that Monocotyledons must have descended 

 from aquatic Dicotyledons. 



Many fossil plants of the Coal and later periods have been found 

 which bear seeds, without carpels, possessing as well, both in their 

 foliage and the internal structure of the stems, features which suggest 

 their origin from Ferns. One of the groups is called Pteridosperms, 

 i.e. " Seed-ferns." In these the spores of Ferns are replaced by pollen- 

 grains, and the normal female structures are represented by ovules 

 only, which become seeds. 



Fossil plants of the Secondary Epoch were evolved from those of 

 the Primary, which was closed soon after the Coal period. The great 

 family of the Secondary Epoch, besides the Pteridosperms and the 

 forerunner of the existing Cycadeae, was the seed-bearing Cordaitales. 



The prevailing forms of the inflorescences were catkins or cone-like 

 structures consisting of bracts or scales bearing, or associated with, 

 anther-cells, and ovules only. 



There are only three families of Gymnosperms now existing, one, 

 the Coniferae, having the largest number of genera and species, includ- 

 ing the Pines, Junipers, and Cypress of the northern, and Araucarias 

 of the southern, hemisphere. The other two have but few members. 

 Thus the Cycadaceae has nine genera, while the Gnetaceae has only 

 three, viz. Gnetum, Ephedra, and Welwitschia. 



In no case can the actual line of descent of any living Gymnosperm 

 be proved from extinct plants ; but there are several structures in each 

 which strongly resemble one another, both in the vegetative organs — i.e. 

 the roots, stems, and leaves—on the one hand, and in the reproductive 

 organs on the other. 



For a complete comparison the reader must consult Dr. D. H.~ 

 Scott's Studies in Fossil Plants, but the following points may be 

 here noticed. 



If we take Ferns as our starting-point, much Fern-hke foHage has 



