CHAPTER XXX 
SEED-BEARING PLANTS (Concluded) 
MONOCOTYLEDONS 
425. General Characters. The monocotyledons are, 
in almost every respect, of simpler structure than the 
dicotyledons. As the name indicates, the embryo has 
only one cotyledon; the parts of the flower are usually 
in threes or sixes, but never in fives, as in dicotyledons; 
the leaves are, with rare exceptions, parallel- veined, 
and the early ones are always alternate on the stem. A 
cross-section of the stem shows that the fibro-vascular 
bundles are not arranged in a circle about a central 
pith (exogenous type), but are distributed irregularly 
throughout the parenchyma (endogenous). There is no 
layer of perennial cambium, and consequently no cylinders 
of wood and bark are formed each growing season, as in 
the dicotyledons. The general characters of the group 
are illustrated diagrammatically in Fig. 338. 
426. Relation to Dicotyledons. A comparison of the 
monocotyledons with the more highly developed dicoty- 
ledons raises at once the question as to whether the former 
are the more ancient forms from 'which the dicotyledons 
have been evolved, or whether dicotyledons are the more 
primitive, in order of development, and the monocotyle- 
dons derived from them by reduction and simplification. 
There is evidence on both sides of this question, which will 
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