404 MR. B. CLARKE ON THE EMBRYOS OF ENDOGENS 



fuiTOw on its surface, as in Avena and Sordeum. The embryo of Sordeum vulgare is in 

 this character much like that of Cymodocea Webbiana, as figuredby Ad. de Jussieu*, the 

 position of its leaves being precisely the same ; so that the evidence of the identity of the 

 embryo of Zostera with those of the Graminacece appears to be complete, and the com- 

 paratively large radicle of this genus and its allies may be regarded as supplying the place 

 of tlie deficient albumen. 



As a further argmnent that the apparent cotyledon of the Graminacece is a radicle, it 

 deserves remark, that in germination it scarcely enlarges, and its smaller lobe, by some 

 botanists regarded as a second cotyledon t, also remains almost stationary ; whereas the 

 stipulary process of the cotyledon, which occupies the same position in Smilacina, Tamils, 

 Iris, and Canna, grows in favourable circumstances so as to be as long or longer than the 

 cotyledon, or even as long as the seed, and sometimes forms a sheath for the young stem. 



In this view of the structure of the embryo of the Graminacece, the second or rudiment- 

 ary cotyledon, which is a minute body, usually referred to as being alternate with, and 

 rather lower down than the larger (fig. 20 b), is the smaller lobe or process of a two-lobed 

 radicle, as in Zostera (fig. 8 «) ; so that the division of flowering plants by Ray into Mono- 

 cotyledonous and Dicotyledonous is quite correct, and the Endogens are separated from 

 the Exogens more completely by this character than by any other. 



For the piu'pose of fm-ther explanation as regards the germination, the position of the 

 first leaf of the plumule, and a proposed division of the Endogens, particular notices of the 

 embryos of the families examined are added. 



Cyperacem. — I have seen germinating the seeds of Cladium Mariscus, of a Cypertts, 

 and of a Carex from Japan, and find that they agree with the Graminacece in having the 

 first leaf of the plumule always next the cotyledon, as at present understood, from which, 

 as this family is so nearly allied, it may be inferred that the embryo has the same struc- 

 ture, and therefore consists of a radicle partially enclosing a cotyledon. There is nothing 

 hi the germination to contradict this supposition, unless it is that the radicle is endo- 

 rhizal in the lowest degree, as no coleorhiza forms, and the nascent spongiole emerges 

 from beneath the surface without a distinct appearance of a rupture of tissue taking 

 place. This is the only family I have observed to agree with the Graminacece in the 

 altered position of the first leaf of the plumule, but it not improbably occurs in other 

 glumaceous Endogens, as Restiacece and Desvauxiacece. 



Zosteracece. — The embryo of Zostera marina has been accurately figured by Richard % : 

 the cotyledon is seen elevated on a cauliculus, and the position of the plumule is distinctly 

 shown, and even the smaller lobe or process of the radicle is faintly indicated, but it 

 is imperfectly seen in consequence of the embryo being closed ; but its endorhizal cha- 

 racter does not appear to have attracted notice. This, however, is quite obvious, as the 



* Ann. des Sciences Nat. 2'°*serie, xi. Bot. pi. 17. fig. 16. 



t Dr. Schleiden states that this is not a second cotyledon, but a part of the cotyledon itself, which he terms the 

 " ligula," and regards it as being of the same nature as stipules, to which it certainly has a close resemblance ; but, as 

 it does not enlarge in germination, it wants one of the characters of stipulary processes, as far as my observation has 

 extended. {Vide Schleiden's Principles of Scientific Botany, translated by Dr. E. Lankester, p. 272.) 



J Ann. du Museum d'llist. Nat. tom. xvii. pi. 9. figs. 47,48. 



