216 
ORGANOGRAPHY. 
BOOK 1^ 
ideas, however, Richard was manifestly wrong, 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 writer, Lestiboudois, would call dicoty- 
ledons exoptiles, because their plumula is naked ; and monoco- 
tyledons endopfiles, because their plumule is enclosed within 
the cotyledon; 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 just 
explanation of the analogy between the embryo of monoco- 
tyledons and dicotyledons has been given ; and I take the 
liberty of reproducing it here : — 
" L 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 ana- 
logous to that of a dicotyledon^ of lohich one of the cotyledons is 
abstracted^ and the other rolled round the plumula 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. 
