Mr. Griffith on the Development of the Ovulum in Avicennia. 6 



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 Myoporince, 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. Wallichf, 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. f PI- Asiat. Rar. iii. pp. 44, 45. 



