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



have called the short central prolongation. But what has been recorded of 

 Santalacece (and the whole of my observations on Avicennia) is opposed to 

 this ; for in all the instances observed, the posterior prolongation is a pro- 

 longation of the posterior end of the sac itself, which obviously would not be 

 the case if the ordinary relations of embryo-sacs to their nuclei existed in 

 j4vicennia. 



Another non-analogous instance may be observed in the gradual protrusion 

 outwards of the young albumen, which is assumable as being at one period 

 entirely interior to the nucleus or ovulum. In all the really analogous in- 

 stances in which the albumen is exterior to the ovulum, it is always exterior, 

 that part of the embryo-sac in which it is developed being protruded long 

 before any albuminous tissue has been developed, which indeed is almost 

 always subsequent to fecundation properly speaking, viz. the completion of 

 certain relations between the anterior end of the pollen-tube and the embryo- 

 sac. 



A third non-analogous instance seems to me presented by the exsertion or 

 protrusion of the cotyledons. Protrusion of the radicular end of the embryo 

 is not, perhaps, uncommon ; but in these cases it may be difficult to ascertain 

 to what extent the protrusion may be due to germination. 



In Cryptocoryne ciliata {Ambrosinia ciliata, Roxb.) however the protrusion 

 takes place long before the cotyledon has acquired its full growth, up to 

 which period moreover it retains its firm fleshy substance. In a Malacca 

 subgeneric form of Cryptocoryne, in which the margins of the spatha cohere 

 into a tube to a great extent, although the plumula is still of considerable size, 

 no protrusion whatever takes place. By the peculiar way in which this is per- 

 formed the embryo becomes almost entirely naked, without however changing 

 the direction it would have had, had it been developed, as it so generally is, 

 within the body of the seed. It is curious that the obliquity in the direction 

 of the young embryo, which is still more extraordinary, takes place at a very 

 early period, for it forms an obtuse angle with the line of the axis of the 

 ovulum and application of the pollen-tubes before there is any indication of 

 cotyledons. For this I do not see any appreciable reason, mechanical or other- 

 wise, though it would perhaps be amiss to overlook the comparative density 

 of the axis of the ovulum in endeavouring to account for the protrusion of 



