90 MR. MIERS OU THE OUTER FLESHY COVERING OF THE SEED 



"Teater probability, that the extraneous coating is produced from the funicular cord, 

 rather than from the foramen or micropyle of the priniine, and in such case the arUlode 

 would not differ from the aril. 



I have had no opportunity of examining the ovule during its growth, but have lately 

 observed ripe and living seeds of Euonymus Europceus. Here the outer coating is entire 

 fleshy and scarlet, with a smooth inner skin, and we find beneath it, another polished, 

 thinner, though somewhat fleshy tunic, that closely adheres to the seed. If this tunic be 

 removed cai-efuUy from the thin pergameneous testa, it will be found to consist of two deli- 

 cate reticulated pellicles, having cellular and fleshy matter interposed between them, the 

 raphe being completely immersed in its substance, in the form of a simple cord, which 

 originating at the basal hdlum, proceeds along its face to the apex, where it pierces the 

 inner pellicle of this tunic, passes into a small opaque speck in the summit of the testa 

 (the diapyle), and is lost in the chalaza of the inner integument which is adherent to the 

 shell. Here we have denionstrative evidence of the nature of these several envelopes ; 

 the outer coat is manifestly a true and entire arU, for we cannot suppose it to be a deve- 

 lopment of the primine, that is to say, an extension of its exostome, as Dr. Planchon 

 almost doubtfully concluded, because it is altogether free from, and exterior to a more 

 internal tunic which encloses the raphe : it follows, therefore, as a necessary consequence, 

 from the position of the nourishing vessels, that it must be a production emanating from 

 the main placenta or a growth from the funicular support of the seed. The fleshy 

 epidermoid tunic which encloses the raphe, and which immediately invests the pergame- 

 neous shell, appears to be an arilline, resulting from the growth of the placentary sheath : 

 the thin pergameneous sheU is, of course, the true testa, marked at its base by a small 

 prominent nipple, close to the hilum, which is no doubt the thickened border of the true 

 micropyle figured by Dr. Planchon, and from which he inferred that the growth of the 

 arU had emanated : the apical speck through which the vessels of the raphe penetrate, is 

 the diapyle : it is hardly necessary to add, that the radicle of the embryo, enclosed in 

 albumen, points to the micropyle, while the extremities of the cotyledons are directed 

 towards the diapyle. I do not find the aril pervious in the apex, as stated by Gsertner, 

 and as figured by Dr. Planchon in another species, although this, no doubt, sometimes 

 occurs ; but in the instance above mentioned, the inner skin of the tunic, though slightly 

 crumpled, is entire, while its outer pellicle is deeply plicated in flattened folds, so that 

 the arU appears cleft into numerous fissiu-es externally. 



Among the many interesting facts detailed by Dr. Planchon in the work just quoted, 

 we meet {loc. cit. p. 25) with an accoimt of the circumstances under which the seeds of 

 Opuntia become covered by two distinct extraneous envelopes, both exterior to the testa : 

 the first is a somewhat thin, hard, coriaceous tunic, according to his observations ; the 

 second is a soft, mucilaginous, pulpy coat by which the former is encircled. The growth 

 of the former was traced by Dr. Planchon fi-om the period of the anatropal inversion of 

 the ovule, which was carried to an extent of a complete gyration, so that the placentary 

 sheath I have before described, appeared at first like an annular band around the 

 periphery of the ovule ; from this ring, on both sides, membranaceous expansions were 

 seen gradually to extend themselves over the intervening spaces, until they met in the 



