OF THE RAPHE IN SEEDS. 101 



the natui'c of the two thin memhranacoous plates, or cellular strata, that line the cavity 

 of the albumen, as before (lescril)cd, and I tliink these may be referred, with little doubt, 

 as we shall see in other well-authenticated eases, to the existence of a large persistent 

 embryo-sac which has not been absorbed, as it usually is in most seeds. In the case in 

 question, at the upper extremity of this cavity, the embryo only one quarter of its length 

 is found, and here the radicle, pointing upwards, terminates in a long mucronate point, 

 which is a kind of suspensor, by which it is pendent in the mouth of the cavity, and where 

 it is enveloped in a small quantity of glutinous matter, which Knes the internal surface of 

 the sac. Instances of the existence of this cavity in the axis of albuminous seeds are not 

 unfrequent, but the discovery that it originated in the persistence of the embryo-sac is 

 due to Mr. Brown (App. King's Voy. p. 21). 



The first consideration that arises is the question whether the existence of this persistent 

 embryo-sac has any necessary connexion A\ith, or has had any share in producing the phse- 

 nomenon of the retroversion of the raphe, and the inversion of the embryo in regard to it, 

 in the manner before stated ; whether the two latter unusual circumstances are independent 

 of each other, or whether they are necessai-ily connected. The only method of forming 

 any conjecture on this head, is to search for facts that have any collateral bearing on the 

 question. In Diospyros we meet with a parallel case of a large ca\'ity in the middle of 

 an albumen, which is open at the hilum, and is in like manner lined with an adherent 

 embryo-sac ; the embryo is found in the outer end of the much larger cavity, the end of 

 the radicle almost protruding out of its mouth : the albumen is deei^ly divided into 

 numerous lamelliform folds, as in Anona, and is covered by two thin integuments, of 

 which the inner one is plicated within the interstices of its lamellar clefts, while a distinct 

 raphe, adliering to the outer integument, proceeds along a groove formed in one of its 

 marginal sides, from the basal liilum to the summit, or opposite cotyledonary extremity, 

 where it disappears. We have here therefore a parallel instance of the existence of an 

 open cavity in the albumen, Kned with the embryo-sac, but this cu'cumstance is accom- 

 panied by the presence of an ordinary raphe, whUe both the seminal tunics and the 

 embryo have gone thi-ough the usual process of anatropal inversion. 



In Anona we meet with a complete peripherical raphe, as in Stemominis, but the 

 embryo-sac has disappeared; there is therefore no cavity, as the embryo lies tightly 

 imbedded in the substance of the albumen, and the radiciilar end of the embryo, vnXh. a 

 very short mucronate point, or suspensor, is directed to the spot where the raphe, after 

 completing an entire circuit round the periphery of the seed, disapjiears close to the hiliim. 

 In this instance we find that a complete gyration of the original tunics, as indicated by 

 the raphe, and only a semi-gyration of the embryo, have taken place ; thus offering a 

 perfect analogy with the structure of Stemonurus, excepting the presence of the embryo- 

 sac and its accompanying cavity. These two instances seem to prove that the presence 

 of this albimainous cavity and the complete gyration of the raphe do not necessarily 

 accompany each other, and they leave us as much in the dark as ever, regarding the cause 

 of the phsenomena observed in the seed of Stemonurus. 



In Opimtia we have another example of a completely annvdar raphe, but the embryo, 

 imbedded in a small quantity of albumen, is quite campulitropal : the raphe after com- 



