28 ESSENTIALS OF BOTANY 
leaf-like, as they do, for example, in the four-o’clock, the 
morning-glory, and the buckwheat; but in the seeds of 
the grains (which contain endosperm) a large portion of 
the single cotyledon remains throughout as a thickish 
mass buried in the seed. In a few cases, as in the pea, 
there are scales instead of true leaves formed on the first 
nodes above the cotyledons, and-it is only at about the 
third node above that leaves of the ordinary kind appear. 
In the bean and some other plants which 
in general bear one leaf at a node along 
the stem there is a pair produced at the 
first node above the cotyledons, and the 
leaves of this pair differ in shape from 
those which arise from the succeeding por- 
tions of the stem. 
37. Classification of Plants by the Number 
of their Cotyledons.— In the pine family 
the germinating seed often displays more 
Hage eee than two cotyledons, as shown in Fig. 12; 
nating Pine, | 12 the majority of common flowering plants 
the seed contains two cotyledons, while in 
the lilies, the rushes, the sedges, the grasses, 
and some other plants there is but one cotyledon. Upon 
these facts is based the division of most flowering plants 
into two great groups: the dicotyledonous plants, which 
have two seed-leaves, and the monocotyledonous plants, 
which have one seed-leaf. Other important differences 
nearly always accompany the difference in number of 
cotyledons, as will be seen later. 
co 
co, cotyledons. 
