PHANEROGAMIA, 253 
nourished by the starch in the cotyledons, which in this 
species remain during the whole process of germination 
beneath the ground enclosed in the seed-coat. In the com- 
mon Field-bean (Phaseolus) the germination is the same 
excepting that the stem elongates below the cotyledons 
and brings the latter above the ground. 
531. The seed of the Castor-oil Plant contains a large 
embryo surrounded by a thin 
layer of endosperm (Fig. 141, 
I). In its germination the 
root and stem below the coty- 
ledons elongate, and thus bring 
the seed-coat with the con- 
tained cotyledons above the 
ground (Fig. 141, ZZ). The 
cotyledons remain within the 
seed-coat until they have ab- 
sorbed all of the endosperm; 
when this is accomplished the 
empty seed-coat falls away, and a feat of a Dioomleden, showing ve: 
the freed cotyledons expand Deo eoe cet 
and assume to some extent the function of ordinary foliage- 
leaves. 
532. The venation of the leaves of Dicotyledons is easily 
studied by macerating them so as to remove the soft tissue, 
leaving only the fibro-vascular bundles. While there is as 
a rule a general likeness between them, there is yet an 
almost infinite diversity in the details of structure. The 
general disposition of the smaller veins is well illustrated 
by Fig. 142. 
533, There are now known upwards of 78,000 Dicotyle- 
dons, showing every degree of development from minute 
