1914] COULTER & LAND—MONOCOTYLEDONY 517 
of growing points has not been traced, and the general conclusion 
has been reached that the terminal cell forms the single cotyledon. 
An examination of the stages between the filamentous proembryo 
and the apparently terminal cotyledon has shown that this con- 
clusion has been taken for granted rather than tested. It is obvious 
that a massive proembryo is formed before growing points appear. 
The terminal cell of the filamentous proembryo of Sagittaria devel- 
ops a mass of tissue whose meristematic peripheral cells develop a 
ringlike cotyledonary sheath, which in the growing seedling is 
still recognizable as an 
extremely narrow ring 
opposite the functional 
cotyledon. Just within 
this sheath, opposite the. 
functional cotyledon, is a 
plate of cells, one or two 
cells thick, occupying the 
site of the second coty- 
ledon which started as a 
second growing point in 
the cotyledonary zone. Fic. 30.—Sagittaria variabilis: transverse 
This plate merges with the _ section immediately above the cofyledonary 
base of the sheath and the ring; a, rudiments of second cotyledon (?); 
150. 
Orv 
RHE 
first leaf, and in one in- 
stance was observed to extend upward 160 yw, and ended in two 
points (fig. 30). This vestigial structure may be interpreted vari- 
ously, but it seems most natural to regard it as a vestige of the 
second cotyledon. In Sagittaria and Alisma the “ growing point”’ 
of the stem has been traced to a definite plate of cells beneath the 
cotyledon. This plate of cells, however, is not the stem primor- 
ium, but the primordium of the first leaf. The “notch” so 
characteristic of these embryos is developed by the checked 
growth of a cotyledon primordium on one side of the coty- 
ledonary sheath, and at the base of this notch, which is really 
between two cotyledon primordia, the first leaf develops. 
The conclusion is that in both Monocotyledons and Dicoty- 
ledons a peripheral cotyledonary zone gives rise to two or more 
