AND THEIR GERMINATION. 403 



and this, I believe, offers a practical explanation of the nature of the two portions of the 

 cotyledon (as at present understood) of Triticum, Oryza (fig. 20 a, b), and other Grami- 

 nacew, in which traces of a stipule-Uke process exist, regarded by some botanists as a 

 second cotyledon. The two portions of the ridge of the embryo of Buppia consist of, 

 1, the larger portion, which forms nearly the whole of the ridge ; and 2, a small process, 

 which fills up a notch in it, and which is always in apposition with the membrane which 

 conceals the plumule, and is therefore always next the fissured or marginal side of the 

 cotyledon* (fig. 6). There is, however, no further difference between Zonnichellia and 

 Rupjna, the first leaf of the plumule being dii'ectly away from the cotyledon, as in that 

 genus f. 



Again, passing on to Zostera, Ave find in Z. marina (figs. 7, 8, 9, & 10) all the parts of the 

 embryo of Ruppia much enlarged ; thus the ridge, which is there but feebly marked, has 

 become an enlarged two-lobed body, appearing when artificially opened almost like a two- 

 lobed cotyledon, and the second portion of the ridge before alluded to, which in Miippia 

 is only a minute body, has become sufficiently prominent to look like a second cotyledon 

 (figs. 8 & 9 rt). The cotyledon has become elevated on a cauliculus, which is cuiwed (fig. 8) ; 

 but tliis is the only difference between it and the embryo of Buppia, as the smaller lobe or 

 process of the radicle is opposite the membrane concealing the plumule, as in that genus 

 (fig. 9 a). The cotyledon becoming elevated on a cauliculus is not uncommon, as it occui-s 

 in the Iridete, Juncacece, Allsmacefe, &c., and is afterwards fm-ther noticed. 



If this is admitted as the only practical explanation of the structure of the embryo of 

 Zostera marina, it appears to follow that the same explanation is the only mode of 

 axjcounting for the relative position of the parts of the embryo of the Graminacece ; for 

 the cotyledon, both in Buppia and Zostera, being next the larger lobe of the radicle, we 

 should expect to find it so in the Graminacece, if the apparent cotyledon is in reality a 

 radicle, and this I have foimd to be the case in both British and exotic genera (fig. 20). 

 All the parts of the embryo have precisely the same relation to each other ; and in Zea 

 Mays the cotyledon (plumule as at present understood) in germination becomes elevated 

 on a caidiculus (fig. 21 a), making the embryo in aU respects like that of Zostera marina, 

 except that it wants the minute secondary lobe, which is, however, present in Triticum, 

 Avena, and Oi'i/za (fig. 20 b). Zostera also further agrees with the Graminacece in being 

 endorhizal in a remarkable degree, as afterwards noticed ; from which it might almost be 

 anticipated that the structure of their embryos would prove to be the same. 



Most of the Graminacece I have seen also agree with Buppia and Cymodocea in the 

 cotyledon (plumule as now understood) not being enclosed by the radicle, but lying in a 



* This small process is distinctly figured by Richard in Ruppia maritima, and his figures correctly show also its 

 position relatively nith the margmal side of the cotyledon. {Vide Ann. du Museum d'Hist. Nat. torn. xvii. pi. 9. 

 figs. J3, 58.) 



t Cymodocea Webbiana and Posidonia Caulini, as figured by Ad. de Jussieu, form a connecting link between 

 Ruppia and Zostera : in Posidonia the cotyledon is more than half enclosed in the upper part of the radicle, and 

 the position of the cotyledon is distinctly shown m both of them by the plumule being exposed ; and they cannot be . 

 supposed to differ in this character from Ruppia and Zostera. (Vide Ann. des Sciences Nat. 2"' serie, xi. Bot. pi. 1 7. 

 figs. 1,5, 16.) 



3g 2 



