274 
MORPHOLOGY 
Among certain plants without chlorophyll (Monotropa, etc.) the 
embryo is very simply organized, consisting of a few cells, the differ- 
entiation into body regions proceeding during germination. 
Monocotyledons. The embryo of Alisma or of Sagittaria is most 
commonly used to represent the monocotyledonous embryo. The pro- 
embryo is usually a filament of three cells (figs. 609, 610), the terminal 
cell forming the cotyledon. The middle cell begins a series of divisions, 
some of the resulting cells forming the stem tip, hypocotyl, and root 
tip, and the others belonging to the suspensor (figs. 611-617). In 
Ftos. 614-617. Further development of embryo of Sagittaria: stages later than 
the series shown in figs. 609613; x, enlarged basal cell; y, middle cell, giving rise 
to stem-tip (s), hypocotyl (A), and some suspensor cells; , the terminal cotyledon. 
After SCHAPFNER. 
this case, also, the boundary between embryo and suspensor is es- 
tablished by a division of the second cell of the proembryo, which con- 
tributes both to the embryo and to the suspensor (fig. 617); but in this 
monocotyledon type the whole of the embryo except the terminal coty- 
ledon is derived from the second cell. The basal cell of the proembryo 
usually becomes very much enlarged, forming the conspicuous part of 
the suspensor (figs. 616, 617). The notable monocgtyledonous feature 
is the terminal cotyledon and the laterally developed stem tip, which 
appears in a notch developed in the side of the axis of the embryo (fig. 
