186 Mr. Griffith on the Ovulum o/'Santalum, 



uncommon : it is usually, I believe, considered to be limited to antitropous 



ovula ; but from the consideration of Galium, Callipeltis and Osyris, I am 



inclined to believe that changes in direction affect nucleary ovula similar to 



those affecting- more complete ovula, so permanently established by M. Mir- 



bel*. This suppression having first been made manifest in Santalacece, it 



naturally became a subject of consideration whether it did not exist in similar 



placentations of certain other natural families, of which Olacinece, certain 



Ferbenacece and Avicennia are marked examples. On this subject my direct 



observations are confined to Congea ; and although these are incomplete, I am 



led to believe that there is not any connexion between this mode of placenta- 



rion and this mode of suppression. It is curious, however, that the ovula of 



the above instances, so far as I am acquainted with them, simulate at the 



period of expansion of the flower in a sufficiently marked manner the ovula of 



Santalacece. Of the reduction of the same organ to the embryonary sac, I 



believe I was the first, and am the only advocate ; my reasons will be found 



detailed in the following section. 



3. On the Embryonary Sac. 

 There appears to be little definite about the sac of the embryo, either in 

 period of development, situation or structure! ; but ordinarily it may be recog- 

 nized as the sac existing within the nucleus, and as that in which the embryo 

 is developed. I know of no positive character that can be assigned to it; for 

 I have reason to believe that in Xanthium a second sac is to be found ; and to 

 say nothing of it, Oyris shows that the embryo is occasionally developed 

 outside it J. 



. S ^ a ' th °" gh * " ery > m *? ° hs *™' ** there is no reason why such may not be the ease 



t See Schleiden's Memoir, op. cit. p. 243. 



I It has, I believe, been supposed by some, particularly by M. Brommiart t„„t n.^, tn 

 tophyllum presents a similar anomaly. But I believe it Jill be ioZ T T n t ^ "' 



Na iades the appearances are due Ja particular Z^^X ^^ "* «» 

 the embryo, in conjunction with a great degree of tenuitv of A if ! " ^'^ ° f 



lopment. ^ lty ° f the sac ltself ™ d * rapidity in its deve- 



