Mr. Grirritx on the Development of the Ovulum in Avicennia. 5 
the albumen, and perhaps for the production of the lateral posterior pro- 
longation. 
The extension of the vascular fascicle so far into what has been considered 
the ovulum, leads me to doubt the real extent of this organ. I cannot recall 
to mind any instance in which the vascular supply of the ovulum is prolonged 
into the substance of the nucleus. A similar doubt is suggested by the extent 
of the head of the embryo-sac inside the ovulum ; for this sac in general, during 
the development of the albumen and embryo, is made gradually to encroach 
upon the nucleus, by which this originally solid cellular body becomes gene- 
rally reduced to a mere cellular membranous covering, or possibly to be 
entirely obliterated. But whatever may be the real extent of the ovulum, the 
nucleary form of which is only physiologically distinguishable from the pla- 
centa, the co-existence of a vascular fascicle with the posterior prolongation 
in Avicennia seems to me to be against the opinion of these curious extensions 
being of a chalazal nature. 
I was not able to ascertain clearly the absolute relations with the embryo- 
sac established by the pollen-tube after it had reached the sac, still less the 
absolute relations which the end of the pollen-tube bore to the nascent embryo. 
All the indications however furnished by my sketches are in favour of the 
penetration of the pollen-tube into the sac, as far as the spot in which the 
embryo makes its first appearance. 
Attention to a peculiarity between the direction of the unimpregnated ovu- 
lum and that of the seed in Avicennia was first pointed out by Mr. Brown in 
his * Prodromus *,' in which it is ascribed to the fecundated ovulum becoming 
erect. This would manifestly make the radicle superior; but if the ovulum 
were of the same nature as in Myoporine, to which Mr. Brown's remarks 
seem to refer, it would as obviously make the radicle inferior. In a sub- 
sequent account given by Mr. Brown through Dr. Wallich+, the erection of 
the seed is attributed to an elongation upwards of the body of the seed, the 
(true) apex maintaining its original (inferior) situation. 
The most important difference between this last account and that which I 
have attempted to give, is, that I find the embryo only to be erect; one part 
of the ovulum (the nucleus), from which it is assumable the seed-coat might 
* Op.cit., ed. Nees, p. 374. + Pl. Asiat. Rar. iii. pp. 44, 45. 
