266 BOTANICAL GAZETTE [APRIL 
will finally be developed. Just how many tiers of cells go to 
make up the hypocotyl and root tip it seems impossible to 
determine; in some cases, no doubt, more tiers than in others, 
since the growth upward seems to have no special definite limit. 
A variable number of suspensor cells are developed. Sometimes 
as many as six cells are left for the suspensor, besides the vesic- 
ular cell, after the definite limits of the embryo are determined 
by the completion of the dermatogen around the root tip (fg. 
75). Atthis stage the suspensor is usually broken. The der- 
matogen is thus fully developed before the plerome strand is 
differentiated enough to be recognized. A hypodermal cell of 
the root tip is differentiated, and by transverse division forms the 
initial cell of the plerome strand (figs. 76, 77, 78, 79), while at 
the same time the central primary meristematic tissue is devel- 
oped into the plerome by longitudinal cell divisions. The ple- 
rome and periblem in most cases can be traced downward to 
this initial cell. The calyptrogen is developed by transverse 
divisions of a small number of dermatogen cells of the root tip, 
which by further divisions form a very small root cap for the 
young embryo (figs. 77, 78, 79). 
The arrangement of tissues in the mature embryo is well 
- shown by cross sections. At the apex a single central cell 
appears (fig. 80), and a little farther up the differentiation of 
the plerome strand and periblem are well marked out (fg. 8r). 
A section about through the center of the hypocotyl shows a 
well-marked dermatogen, and inside of this three layers of large 
_ periblem cells with large intercellular spaces. In the center the 
plerome is composed of a bundle of twelve or more long nar- 
row cells, surrounded by a circle of nine or more larger cells 
forming asheath (fig. 82). Finally, a longitudinal section 
through the stem apex shows a very deep cleft with the first 
leaflet already somewhat developed (fig. 83). 
: SUMMARY. oy 
Ss oly eke. the development “ the pollen grain, 
oe sac, and i embeyes of Fens variabilis is the same as e i 
