1914] COULTER & LAND—MONOCOTYLEDONY 513 
farther upward on the side opposite the first leaf, giving the seed- 
ling a slight asymmetry (fig. 17), but soon the sheath becomes a 
symmetrical ring in transverse section (figs. 18 and 19). Each 
cotyledon has two lateral strands, as if the middle one present in 
the monocotyledonous seedling has not been laid down. The 
second leaf is also well developed, so that six strands approach the 
cotyledonary plate (figs. 21-23). These gradually converge, the 
phloem of the cotyledonary strands uniting with that of the first 
leaf (fig. 23), and lower down with that of the second leaf (figs. 24 
and 25), but the xylem does not fuse until farther down (fig. 26). 
As in the monocotyledonous seedling, the cotyledonary plate is a | 
siphonostele, and the strand of the first leaf continues directly as 
one of the poles of the triarch root, and lower down divides, result- 
ing in a tetrarch root. - 
So far as the vascular strands are concerned, the two seedlings 
differ in the number laid down in the cotyledons. The larger single 
cotyledon contains three strands, while each of the smaller cotyle- 
dons of the dicotyledonous seedling contains two strands. The 
organization of the cotyledonary plate and of the root poles is the 
same in both cases. 
It is obvious that this difference in the number of vascular 
strands does not determine the development of one or two cotyle- 
dons; the number of strands is simply a result of. the development 
of one or two cotyledons; for vascular strands are differentiated in 
the tissues of a growing organ. It seems clear, therefore, that the 
appearance of one or two persistently growing points in the coty- 
ledonary region of the proembryo determines the monocotyledonous 
or dicotyledonous condition; and that in Agapanthus the number 
of such growing points is variable. 
In comparing the two seedlings, a suspicion might arise that 
the so-called dicotyledonous seedling, with its two leaves as well 
as its two cotyledons, is a case of the fusion of two embryos, or 
rather two produced by a single proembryo. This possibility has 
not been traced through in detail, but the vascular situation just 
described shows that the dicotyledonous seedling is merely a slight 
modification of the monocotyledonous one, and gives no Dio srg 
of the “fusion” of two embryos. 
