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 ascertamed 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 sae 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 Cucurbitacee, 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 papille ; 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 Narthecium, Bartsia and Euphrasia. 
In the 16th volume of the ‘Transactions of the Linnean So- 
ciety,’ Mr. Brown, in his essay on the Mode of Fecundation in 
the Orchidee, 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 
a 
