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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 



