186 Mr. Griffith on the Ovulum of Santalum, < 



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

 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 

 Verbenacece 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- 

 tion 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, Osyris shows that the embryo is occasionally developed 

 outside itj. 



* M. Schleiden in his memoir " on the Organization of Phsenogamous Plants," Lond. and Edinh. 

 Phil. Mag., 1838, p. 185, appears to think that in Santalaceee the ovulum is an "ovulum anatropum," 

 and says that he had never met with an instance of reduction to a nucleus in any other modification of 

 this organ, although he very justly observes, that there is no reason why such may not be the case. 



i' See Schleiden's Memoir, op. cit. p. 243. 



X It has, I believe, been supposed by some, particularly by M. Brongniart, that the embryo of Cera- 

 tophyllum presents a similar anomaly. But I believe it will be foimd that in Ceratophyllum and certain 

 Naiades the appearances are due to a particular development of the cells of the funicle or suspensor of 

 the embryo, in conjunction with a great degree of tenuity of the sac itself and of rapidity in its deve- 

 lopment. 



