[ 401 j XXXIII. On the Embryos of Endogens and their Oermination. By Benjamin Clarke, Esq., F.L.S. Read June IGtb, 1859. It is now some years since L. C. Richard, in his original and very accurate work, the ' Analyse du Fruit *,' divided phanerogamous plants, with reference to their germina-tion, into Endorhizse and Exorhizse; hut notwithstanding that exceptions to the exo-rhizal character as regards the secondary radicles have been repeatedly observed in exogenous plants, and its universality in the primary radicle doubted, yet in general works in which germination is referred to, this division is considered practicable, and the Endogens also are stiU regarded as being constantly endorhizal. In examining the germination of the Endogens, however, for the pui'pose of ascertain-ing the position of the first leaf of the plumule relatively to the cotyledon, the primary radicle proved, contrary to my expectation, to be perfectly exorhizal in the greater nimiber of instances, and so obviously without any trace of a sheath (coleorhiza) in Iris, Alstro-meriu, Smilaciua, Butomus, Tamils, and Arum, as to place the fact beyond question. The secondary radicles in the Endogens, it is true, are usually, if not always, endorhizal, inasmuch as they protrude from beneath the cellular integument common to the primary radicle and young stem, although no sheath may be present ; but this is a character also common to certain Exogens, as Menyanthes trifoliata, in which the secondary radicles and their branches not only protrude from beneath the sm-face, but have small sheaths at then-bases ; and some of the more remarkable instances of this kind have been described as occui-ring in the germination of Baminculacece, Composite, and other families. The germination of Nuphur liitea also presents another remarkable instance in which the primary radicle is perfectly exorhizal f, but the secondary radicles above it are endo-rhizal, the elongated sheaths remaining attached during the early stages of growth. (PI. LXVIII. figs. 1, 2, & 3.) Einding, therefore, the Endogens to be frequently exorhizal, as many of them as oppoi--tunity afforded were germinated, and the probability appears to be that the primary or true radicle is known to be endorhizal (with two additions afterwards noticed) only in Marantacem, Commelynucece, Cyperacew, and Graminacece. To these families should perhaps be added Naiadece, since Richard has figured ZannichelUa palustris as having all the appearance of an endorhizal germination ; but whether they are endorhizal may be a question, because the embryos of some genera in their radicular portion do not differ materially from those in which the germination is exorhizal ; and also in the embryo of Zanniehellia no trace of a sheath is perceptible in a longitudinal section, while in Zostera * Demonstrations, ou Analyse du Fruit, 1808 ; H. A. Duval, Ed. + The germination of Nymphtea alia has been referred to as being endorhizal, but as I have not liad an opportunity of seeing it, this observation on Nuphar lutea was made with the greatest care ; a fringe of minute radicles gives it in some degree the appearance of being endorhizal, but on examination it proves to be entirely an appearance. VOL. .KXII. 3 G
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