OF THE RAPHE IN SEEDS. 105 



testa, and where the raphe terminates. Gacrtner farther affirniis that the amniotic fluid 

 is secreted at this point of the gangylode, which is also the opinion of Mr. Brown (Linn. 

 Trans, x. 37). This point is sometimes distinguished by a peculiar protuberance, within 

 the cavity of the main body, ^\ hich Miz'bel calls the chalazal appendage (appendice chala- 

 zienne), and he says that at this point the embryo-sac is first developed. We are indebted 

 to Mr. Brown (Append. King's Voyage) for nearly all the information we now possess 

 respecting the nature and origin of the several parts of the ovule, and the changes they 

 undergo dm-ing the growth and jierfection of the embryo, and it is impossible to estimate 

 too highly the importance and merit of these admirable observations, the truth of which 

 is unquestionable. A large share of credit is due to M. Brongniart, who about the same 

 time, and to M. Mirbel, who three years afterwards, contributed many important facts on 

 this sul)ject, all confirming the preWous observations of Mr. Brown. The latter able phy- 

 siologist brought together aU this information in his two celebrated memou's " On the 

 Development of the Ovule," &c. (Mem. Acad. Sci. Paris, ix. p. 609 & 629) : he there 

 gives a regular nomenclature to the several parts of these developments, and reduces all the 

 evidence into a beautiful system, which has been adopted by aU, and which has remained 

 unquestioned now for nearly thii-ty years ; but true as it may be in a general point of 

 view, the evidence I have now brought together wUl show that the laws considered so 

 universal, fail in their application in many cases, perhaps in far more numerous instances 

 than are here offered, or wUl at fin'st be credited. The existence of the two outer tunics, 

 the primine and secundine, had long been known ; but their remarkably peculiar cupuliform 

 shape, seen alone in a very yoimg state, was first shovm by Mirbel, and by him also the 

 metamorphoses of the main body of the ovule, called ' chorion ' by Malpighi, and ' nucleus ' 

 by Mr. Brown, who first explained its functions, were now more fully demonstrated. 

 Mirbel, who called this ' nucleus ' the ' tercine,' showed that it is Kned with a pecuUar 

 tissue, which sometimes becomes transformed into another tunic, the ' quartine,' and which 

 in Statice he describes as forming a completely closed vesicle. Another body, which he 

 denominates the ' q\iintine,' is stUl farther developed in the interior of the quartine : this is 

 the ' sacculus colliquamenti ' of Malpighi, the ' amniotic sac ' of Mr. Brown, the ' embryo- 

 sac ' of M. Brongniart, the point of origin of which has been noticed above ; when this 

 vesicle is wanting, which perhaps more frequently happens, it is then the quartine that 

 becomes resolved into the embryo-sac. According to Mii'bel, one end of this sac is 

 attached to the point of the gangylode, while the other is fixed to the summit of the 

 tercine or quartine : it gradually swells from top to bottom, thrusting away the tissue 

 that surrounds it. Brongniart first noticed the fact of the descent of the boyaux of poUen- 

 grains, through the stigmatic channel, but failed in tracing their farther com-se, and the 

 mode of their action in effecting the fertilization of the ovule, a discovery due to Amici. 

 According to the observations of more recent physiologists, it is now admitted, that in 

 every case of fertilization of an ovule, the boyau of a pollen-tube descends through the 

 stigmatic channel, and is conveyed through the apical orifices of the primine and secun- 

 dine (the micropyle), and passing through the tercine, thus reaches the embryo-sac, in 

 the summit of which is a small globular body, called by Meyen ' the primary utricle,' 

 which body, consequent on its osculation with the boyau, subsequently swells and becomes 

 VOL. XXII. P 



