1897] PHYLOGENY AND TAXONOMY OF THE ANGIOSPERMS 157 
foliar cell gives rise to the single cotyledon, and the divided 
cell, to the pair of cotyledons. 
Thus far in this discussion the embryology of monocotyle- 
dons and dicotyledons indicates little more than the close rela- 
tionship of the two sub-classes. Will it do more? Are there 
any indications which may help us to answer the question of the 
origin of these two groups? Have dicotyledons been derived 
from monocotyledons, monocotyledons from dicotyledons, or 
both from some common ancestor? It must be admitted that 
on theoretical grounds it is no more difficult to pass from two 
cotyledons to one, than from one to two. Indeed, there have 
been not a few botanists who have suggested the derivation of 
the monocotyledons from the dicotyledons. When, however, 
one compares the two embryos, there is a slight preponderance 
in favor of the view that the structure is a little higher in dicoty- 
ledons than in monocotyledons, The row of undivided cells 
in the embryo of the monocotyledon after the third or fourth 
segmentation is certainly a lower structure than the compact 
mass of cells constituting the ‘‘octant-stage”’ of the dicotyle- 
donous embryo. The cotyledons themselves afford a slight sug- 
gestion as to the relationship of the two groups. It is a well 
established principle in embryology that embryonic stages of 
higher organisms resemble the adult stages of the organisms 
which are lower in the same genetic line. Applying this prin- 
ciple to the cotyledons, we observe that while they bear some 
similarity to the leaves of both monocotyledons and dicotyle- 
ons, the similarity is a little more marked in case of the mono- 
cotyledons. Compare the mostly sessile, often clasping, usually 
elongated leaves of monocotyledons with the cotyledons of 
either class, and contrast these with the mostly petioled, gener- 
ally not clasping, and usually broad-bladed leaves of the dicoty- 
ledons. 
But we must not stop with the embryo plant in this com- 
parison. The young plant continues to pass through what are 
essentially embryonic stages long after it has left the seed, and 
begun its life as an independent organism. In the ontogeny of 
