216 ORGANOGRAPHY. BOOK 1^ 



ideas, however, Richard was manifestly wTong, as is now well 

 known. 



From what has been stated it is apparent that dicotyledons 

 are not absolutely characterised by having two cotyledons, nor 

 monocotyledons by having only one. The real distinction 

 between them consists in their endorhizal or exorhizal germi- 

 nation, and in the cotyledons of dicotyledons being opposite 

 or verticillate, while they are in monocotyledons solitary or 

 alternate. Some botanists have, therefore, recommended the 

 substitution of other terms in lieu of those in common use. 

 Cassini suggests isodynamous or isohrious for dicotyledons, 

 because their force of development is equal on both sides: 

 and anisodynamous or anisohrious for monocotyledons, because 

 their force of development is greater on one side than on 

 the other. Another wi'iter, Lestiboudois, would call dicoty- 

 ledons exoptiles^ because their plumula is naked ; and monoco- 

 tyledons ejidoptiles, because their plumule is enclosed within 

 the cotjdedon ; but there seems little use in these proposed 

 changes, which are, moreover, as open to objections as the 

 terms in common use. 



In the " Library of Useful Knowledge" an apparently j ust 

 explanation of the analogy between the embryo of monoco- 

 tyledons and dicotyledons has been given; and I take the 

 liberty of reproducing it here : — 



" 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 Wlieat 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 Mdth the large 

 flat one, on the opposite side of the plumule. Hence we are 

 to infer that the monocotyledonous embryo of a Palm is ana- 

 logous to tliat of a dicotyledon, of which one of the cotyledons is 

 abstracted, and the other rolled round the plianula and consoli- 

 dated 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. 



