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- 
naceæ, in which traces of a stipule-like process exist, regarded by some botanists as a 
second cotyledon. The two portions of the ridge of the embryo of Ruppia 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 Zannichellia and 
Ruppia, the first leaf of the plumule being directly away from the cotyledon, as in that 
genus f. 
Again, passing on to Zostera, we 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 Ruppia 
is only a minute body, has become sufficiently prominent to look like a second cotyledon 
(figs. 8 & 9a). The cotyledon has become elevated on a cauliculus, which is curved (fig. 8); 
but this is the only difference between it and the embryo of Ruppia, as the smaller lobe or 
process of the radicle is opposite the membrane concealing the plumule, as in that genna 
(fig.9a). The cotyledon becoming elevated on a cauliculus is not uncommon, as it occurs 
in the Zrideæ, Juncacee, Alismaceæ, &e., and is afterwards further 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 
accounting for the relative position of the parts of the stis à V igit = 
th : : Zostera, being next the larger lobe oi the vidi 
e cotyledon, both in Ruppia and Zostera g cotyledon is in reality a 
should expect to find it so in the Graminacee, if the apparent 20 
radicle, and this I have found to be the case in both British and exotic pne å > 
All the parts of the embryo have precisely the same relation » på pénis ael 
Mays the cotyledon (plumule as at present understood) in germination un nn 
on a cauliculus (fig. 21 a), making the embryo in all respects like that o m. 
except that it wants the minute secondary lobe, which is, mad being 
Avena, and Oryza (fig. 20 b). Zostera also further agrees — ft might almost be 
RE, | afterwards noticed ; from 
endorhizal in a remarkable degree, as ve to be the same. 
anticipated that the structure of their embryos would pro Ruppia and- Qymodocea in the 
Most of the Graminaceæ I have seen also ag - b Ge medic but lying in à 
cotyledon (plumule as now understood) not being enclosed by si 
a: : ly show its 
* "This small process is distinctly figured by Richard in zu. are mg EEE xvii. pl. 9. 
Position relatively with the marginal side of the cotyledon. (Vide Ann. du 
figs. 43, 58. i connecting link between 
t E Webbiana and Posidonia Caulini, as figured by M —Ó part of the radiele, and 
Ruppia and Zostera: in Posidonia the cotyledon is more A agri gin and they cannot be 
the position of the cotyledon is distinctly shown in both of them by the p meras ces Nat. 2™ série, xi. Bot. pl. 17. 
Supposed to differ in this character from Ruppia and Zostera. Aisi ds 5 
figs. 15, 16.) da 
