OF THE RAPHE IN SEEDS. 109 



at the point where, according to the laws of structure, the chalaza ought to be found in 

 all cases where a raphe exists : it is precisely in the situation ascribed to the chalaza by 

 Mirbel, in his figure before quoted of the ovule, after the formation of the embryo. It is 

 however only a false chalaza, and is most probably a thickening of the mouth of the 

 micropylo (exostome of Mirbel) of the ovular integuments, a circumstance of frequent 

 occurrence in certain seeds ; or it may possibly be ascribed to a scar of the embryo-sac, at 

 the point where it has broken away from the gangylode, as figured by Mirbel {loc. cit. 

 fig. 10. letter/). That it cannot possibly be the true chalaza, is most evident, because 

 it has had no apparent connexion with the outer crustaceous tunic, which exhibits no 

 corresponding scar or trace of any former connexion at this point ; and still more obvi- 

 ously, because the raphe passes straight across it, without holding the slightest commu- 

 nication with it. The embryo, which has no albumen, fills the whole cavity of the inte- 

 guments in the ripe seed, the radicle being directed towards the liilum and to the 

 terminating point of the raphe, and its extremity being covered by the true chalaza ; its 

 cotyledonary extremity is in the opposite direction, terminating at the areolar micropyle 

 or false chalaza. The fact of the existence of the free cord of spiral vessels as above- 

 mentioned (the i-aphe), riinning between the outer crustaceous tunic and the inner 

 integuments of the seed, was evidently known by Mr. Griffith, who notices it (Posth. 

 Notes, p. 182) ; but he omitted to observe the passage of this thread over the areole, 

 which has always been considered as the chalaza, and also its course round the entire 

 periphery, as well as its termination at the radicular extremity of the membranaceous 

 integuments : the presence of the true chalaza at this point also escaped his observation. 

 I do not find any mention of this curious structure by any other botanist. 



We thus observe the same phsenomena existing in all the genera of the Cucurhitacece 

 that I have described as being found in Stemonurus, Anoiia, and Citrosma, that is to say, 

 where the cord of the raphe makes a complete cu'cuit of the seed, terminating at the same 

 time at the radicular point of the integuments, instead of the cotyledonary extremity, as 

 it ought infallibly to do, according to the acknowledged laws of structm-al development. 

 What has been the nature of the metamorphoses within the ovule, that have produced so 

 manifest a deviation from the ordinary course of structure ? We have it demonstrated 

 on the high authority of Mirbel, that up to the period of the impregnation of the ovule, 

 the raphe, the chalaza, and the primine and secundine (then agglutinated into one coat), 

 had only performed a simple anatropal inversion from their normal position ; but we find 

 that in the interval between this period and the ripening of the seed, aU these parts have 

 experienced a farther circumversion, so as to complete an entire circle, while the embryo- 

 sac, or at least the embryo, has retained the same position which it held at the period of the 

 simple anatropal inversion of the ovule. Mirbel notices, at this last-mentioned period, the 

 fii-st indication of the growth of the arillseform coating over the prioaine, appearing at 

 this epoch as two layers of cellular tissue coating that integument, and Avhich he figures 

 {loc. cit. fig. 10. letter //) : these layers of tissue are unquestionably the rudimentary 

 secretions that subsequently form the arillus, under the crustaceous appearance of a testa, 

 for which it has always hitherto been mistaken : it is doubtlessly owing to the formation 

 of this coating that the subsequent movement of the coats of the ovule has been hidden 



