224 Linnean Society. [November 19^ 



Mr. Griffith states that Avicennia has, like Santalum and Osyris, 

 a free central placenta with pendulous ovula; the same posterior 

 elongation takes place in the embryo-sac ; and the embryo is, at least 

 when matured, external to the nucleus or body of the ovulum. The 

 ovula of Avicennia appear to be nucleary ; their central tissue first 

 becomes denser than the rest, and in this denser tissue, at a period 

 antecedent to fecundation, is found the embryo-sac, having usually 

 an enlarged apex or head and a subcylindrical body. Subsequent to 

 the application of the pollen-tubes to the apex of the sac, and the 

 formation of cellular tissue, the head of the embryo-sac acquires a 

 short prolongation posteriorly in the direction of the axis of the ovu_ 

 lum, and its subcylindrical body is also prolonged posteriorly within 

 the inner side of the same organ. While the albuminous tissue in 

 the head of the sac increases in bulk, and the rudiment of the future 

 embryo is developing, the head enlarges and passes out of the apex 

 of the ovulum, and the prolongation of the subcylindrical body con- 

 tinues to increase in length. At a subsequent period there is formed 

 on the anterior surface of the albuminous mass, now become external 

 to the ovulum, a curved furrow or groove, corresponding with the 

 points of the cotyledons of the young embryo ; and the posterior 

 prolongation of the body of the sac passes backwards into the pla- 

 centa, within which it is divided in a digitate irregular manner. In 

 the next stage the points of the cotyledons protrude through the 

 groove, and as the embryo increases in size they become more and 

 more exposed, the part of the ajbumen situated between the inner 

 cotyledon and the body of the ovulum becoming at the same time 

 enlarged and flattened, and increasing in length equally with the 

 cotyledons themselves. In the mature embryo the radicle alone re- 

 mains imbedded in the albuminous tissue, the cotyledons being quite 

 naked. 



" It is curious," Mr. Griffith observes, " that this prolongation 

 [of the embryo-sac] has only been observed in association with a 

 particular form of the free central placenta. So far as I know," he 

 adds, " it is the only instance of an embryo-sac prolonged posteriorly, 

 it may be said, from two points of its surface." And further : " In 

 all the really analogous instances 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*." 



* In a Memoir by M. Planchon, published at Montpellier, 1844, " Sur les 

 developpements et les caracteres des vrais et des faux arilles, suivi de con- 



