68 THEORY OF MONOCOTYLEDONS. [BOOK i. 



In the Library of Useful Knowledge, the following explana- 

 tion of the analogy between the embryo of monocotyledons 

 and dicotyledons has been given : 



"1. The embryo of an Arum is like that of a Palm, only 

 there is a slit on one side of it through which the plumule 

 easily escapes ; 2. in Rice (Oryza) this slit is very much 

 lengthened and widened ; 3. in Barley the plumule projects 

 beyond the slit, leaving a flat cotyledon on one side; and, 

 4., in Wheat the embryo has the structure of Barley, with 

 this most important exception, that at the base of the plumule 

 in front there is a rudimentary cotyledon, alternate with the 

 large flat one on the opposite side of the plumule. Hence 

 we are to infer that the monocotyledonous embryo of a Palm 

 is analogous to that of a dy cotyledon, of which one of the coty- 

 ledons is abstracted, and the other rolled round theplumula and 

 consolidated at its edges. And this is the view that must be 

 taken of the monocotyledonous embryo in general, all the 

 modifications of which seem reducible to this standard. 



"Thus in Sea- wrack (Zostera marina), of which the embryo 

 is an oblong almond-shaped body with a cleft on one side, in 

 the cavity of which a long flexuose process is placed, the 

 latter is the plumule, and the former at one end the cotyledon, 

 and the radicle at the other; in Ruppia maritima, whose 

 embryo is an oblong body, cut suddenly off at one end, on 

 which a sort of curved horn crouches, the latter is the plumule, 

 and the former chiefly cotyledon ; and so in Frog-bit (Hydro- 

 charis morsus ranse), the embryo of which is an oblong fleshy 

 kernel with a hole on one side, in which there lies a short 

 cylinder, the latter is the plumule, and the former the 

 cotyledon." 



M. Adrien de Jussieu has examined this theory with much 

 ability. By tracing the development of the monocotyledonous 

 embryo, he found that in reality the plumule is enwrapped 

 by the lower portion only of the cotyledon, and therefore he 

 would modify the theory accordingly. "La Theorie de 

 M. Lindley n' est done vraie que pour la partie inferieure ou 

 gaine du Cotyledon, la seule qui s'enroule autour de la 

 plumule ; et la premiere feuille de la pi ante monocotyledonee 

 ne se comporte pas autrement que chacune des autres, dont 



