STRUCTURE.] MONOCOTYLEDONOUS EMBRYOS. 65 



appear at once from the very surface of the radicular extre- 

 mity, and consequently have no sheath at their base. Upon 

 this difference Richard proposed to substitute the term 

 Endorhizffi for monocotyledons, and Exorhiza for dicotyle- 

 dons. Some consider the former less perfect than the latter : 

 endorhizee being involute, or imperfectly developed : exorhizse 

 evolute, or fully developed. Dumortier adds to these names 

 endophyllous and exophyllous ; because the young leaves of 

 monocotyledons are evolved from within a sheath (coleophyl- 

 lum or coleoptilum), while those of dicotyledons are always 

 naked. The sheath at the base of the radicle of monocotyle- 

 dons is called the coleorhiza by Mirbel. Another form of 

 monocotyledonous embryo is that of Arads and their allies, 

 in which the plumule is not so intimately combined with 

 the embryo as to be undistinguishable, but is indicated 

 externally by a little slit above the base (Plate VI. fig. 6. 

 B. e), within which it lies until called into development by 

 germination . 



Mr. Griffith describes a most singular exception to the 

 usual monocotyledonous structure in Cryptocoryne spiralis : 

 " The embryo is of a singular shape. Its descending portion, 

 or cotyledon, is clavate, and nearly entirely inclosed within 

 the nucleus ; the inclosed part separating with that bady 

 exceedingly readily, and subsequently, about the same time 

 of dehiscence of the fruit, spontaneously. The tissue of the 

 inclosed part is firm, and more dense than the short unin- 

 closed part. The exserted portion of the embryo consists 

 exclusively of the base of the cotyledon, of a fleshy, firm, 

 plano-convex body. The plane part is depressed towards the 

 centre, to which the base of the cotyledon is attached. From 

 one side of this the radicle projects, which is still conical and 

 acute, and is always directed from the placenta, and generally 

 outwards, but often laterally, and always more or less down- 

 wards. The circumference of the convex part is entirely 

 occupied by the processes, constituting an enormously de- 

 veloped plumula. These are densely imbricated, intermixed 

 with abortive and rudimentary ones, and of immense length, 

 especially the outermost, which are about one inch long. 

 They are all subulate, with the exception of the two or three 



VOL. II. F 



