8 Dr. G. Dickie on the Physiology of Fecundation in Plants. 



the extremity and not through its whole extent. The objections 

 to the tubes being prolongations from the ovule will lose their 

 force, when we call to mind the remarkable facts ascertained by 

 the late Mr. Griffith respecting the ovule of Santalum. In this 

 plant the nucleus is naked, primine and secundine being absent ; 

 at a certain stage '' a tubular membrane protrudes from the centre 

 of the apex of the nucleus, in which no opening can be detected 

 previously. This tubular membrane passes down at first in the 

 direction of the axis of the ovulum, but becomes immediately re- 

 curved, and passes up one side of the ovulum and in close appo- 

 sition to the placenta -/^ again, " the tubes remain in apposition 

 to the placenta, and continue to be simple, membranous, elon- 

 gated, closed tubes. ^^ (Linn. Trans, vol. xviii. p. 60, &c.) This 

 membranous tube Mr. Griffith believed to be the sac of the am- 

 nios, " which in ordinary structures lines the cavity formed in the 

 nucleus at some period previous to fecundation, and which, at 

 least in its earlier stages of development, is the only coat that is 

 membranous. ^^ M. Ad. Brongniart many years ago announced 

 the discovery in the interior of the nucleus of a special membra- 

 nous tube often prolonged beyond the ovule, and which esta- 

 blishes a communication between the conducting tissue of the 

 placenta and the point where the embryo is formed. This was 

 observed in some Cucurbitacece, in several species of Polygonum, 

 and other plants. The same structure had however been pre- 

 viously discovered by M. de St. Hilaire. These ovule-tubes are 

 probably of more frequent occurrence than has been supposed : I 

 have seen them in great abundance on the placenta of Bartsia 

 Odontites and Euphrasia officinalis : I was unable to trace their 

 origin from the pollen, but had no difficulty in seeing their con- 

 nexion with the ovules, and their adhesion to or rather continuity 

 with the apex of the nucleus. It was at first suspected that they 

 were pollen-tubes ; this idea was soon abandoned when they were 

 found to terminate in blind extremities toward the upper part 

 of the placenta. In young ovules they were seen protruding 

 from the exostome in the form of minute transparent papillae ; in 

 others further advanced their increase in length was very evident. 

 Similar tubes were found in connexion with the ovules in Par- 

 nassia palustris. I believe them to be prolongations of the apex 

 of the nucleus in Nartheciunij Bartsia and Euphrasia. 



In the 16th volume of the 'Transactions of the Linnsean So- 

 ciety,^ Mr. Brown, in his essay on the Mode of Fecundation in 

 the Orchidece, has stated the existence of "mucous cords" or 

 tubes on the placenta of several plants belonging to that family. 

 In the first part of this essay Mr. Brown supposed that these 

 tubes were actually derived from the pollen, but he had not been 



