WOODBURN: EMBRYOLOGY OF REBOULIA HEMISPHERICA 463 
3, 4, 5,6 and 11) indicate that from the hypobasal cell is devel- 
oped the foot and from the epibasal cell the stalk and sporangium 
of the mature sporophyte. 
A third division follows in either the middle or apical cell of 
the tier of three (Fic. 4) which results from the first and second 
divisions. Compare Fic. 5, which shows a tier or series of four 
cells, with Fic. 4. Then follows (Fic. 6) a division in the basal or 
foot cell at right angles to the first three division walls. The 
foot at this stage has become quite dense in protoplasmic contents. 
The order of divisions just described seems to represent the 
usual conditions. Compare, however, Fics. 2-6 with Fics. 7-10. 
In each section represented by Fics. 7 and 9 there is a triangular- 
shaped apical cell, while in Fics. 8 and 10 both apical and basal 
cells of triangular shape are present. FG. 11 represents a slightly 
different condition, in which the foot has become divided into an 
irregular group of cells. 
In no case do we find the same sequence of early divisions as 
described by Cavers (2). In speaking of the early divisions of the 
sporophyte of Reboulia, he says, “The transverse basal wall is 
followed by two sets of nearly equal vertical walls which intersect 
each other at right angles, so that the embryo shows a regular 
octant stage.”’ 
SUMMARY. 
The egg and sperm nuclei are both in a resting condition in the 
earliest stages of fusion. 
Among the Bryophytes little is known concerning the details 
of nuclear behavior during the stages of fertilization. 
The earliest divisions of the zygote are transverse. A longi- 
tudinal series or tier of four cells may be formed. 
Occasionally, however, both apical and foot cells of triangular 
outline may be formed, or the basal cell may divide into an irregular 
group which constitutes the foot. 
Of the first two cells formed, the hypobasal cell evidently 
produces the foot, and the epibasal cell the stalk and sporangium 
of the mature sporophyte. ~ 
NORTHWESTERN UNIVERSITY, 
Evanston, ILLINOIS 
