IN THE CLUSIACEiE, MAGNOLIACEiE, ETC. 91 



centres, and thus formed one complete tunic, which finally assumed the solidity and 

 texture of a crustaccous shell, which he called a "false testa": this again became 

 enveloped by a second placentary extension, in the form of a transparent soft pulp. 

 These facts had been previously authenticated by the careful observations of Gasparini*, 

 who describes, with great apparent accuracy, the curious phsenomena attendant on the 

 growth of the ovule of Opimtla, from its earliest development to the state of its ripe 

 seed. After its anatropal inversion, the ovule is seen suspended by its short funicular 

 cord (podosperm) from the hilum, which cord, in form of a placentary sheath, or thick 

 cylinch-ical filament, is seen to extend itself round it, until it encircles the ovule like an 

 annular ring : from this ring, on each side, a distinct membrane, at first very thin, 

 expands itself by slow degrees, until at length, on both sides, it becomes extended in a 

 complete tunic, over the entire surface of the ovary. After the period of fecundation, he 

 farther obsei'ves, if we watch every now and then the growth of the ovary, during its 

 transformation to the state of seed, we see the tunic just mentioned, as well as its very 

 short podosperm, become covered, little by little, with a pulp. In proof of the fact that 

 the production of this more external tunic originates in the extension of the podosperm, 

 he states that sometimes, in some ovules, from some unknown cause, the above-described 

 annular prolongation of the placentary sheath is not formed, and in such case the seed is 

 not covered with the usual pulpy envelope. Some explanation, however, is here requisite, 

 which I am enabled to give from the examination of the large seed of a species of Opuntia, 

 collected by me in Chili many years ago. This has convinced me of the correctness of 

 the details given by Gasparini and Planchon, with this exception, that the thin pellicular 

 membrane, wliich both actually witnessed in the act of its growth and extension over the 

 primine, and which the latter imagined became converted into the thick osseous sheU, 

 is no other than the intermediate epidermoid tunic, which I foimd still covering the 

 shell. "We may feel assured that the deposition seen of osseous cells, to form the 

 crustaceous shell, took place in the substance of the primine, and not in its arillinar 

 covering, as Dr. Planchon inferred, for Gasparini makes no mention of such an occur- 

 rence. That such is the case, is manifest from the position of the raphe, and it is not less 

 clear, from the phsenomena observed, that the membrane, as they saw it in the progress of 

 its growth, is a production of the placentary sheath, and is therefore of the natm-e of an 

 arilline. So, in like manner, the pulpy envelope emanates from the placentary sheath or 

 funicle ; and that such is really its origin is proved by the curious fact related by Gasparini, 

 that when, as it sometimes happens, the placentary sheath is unformed, no growth of 

 pulpy matter takes place over the seed. Prom the circumstances above detailed, we may 

 safely conclude that the hard crustaceous shell in the seed of Opuntia is its testa, that 

 its annular ring is the raphe, and that the intermediate tunic coating the testa is an 

 arilline ; while the more exterior pulpy envelope, whether originating in the placentary 

 sheath or the funicle, is still an aril, because it is void of spiral vessels. 



Another striking confii-mation of the fact of the gradual increment of the fleshy coating 

 over the primine, is cited by Dr. Planchon, and is the more important, because it 

 occurs in Clima, and bears immediately on the question at issue. In the work before 



* Ossenrazioni intorno alia struttura dcU' arillo. Rendiconto dell' Accad. delle Scienze di Napoli, an. 1843, p. 260, 



n2 



