WOODBURN: EMBRYOLOGY OF REBOULIA HEMISPHERICA 463 



3, 4, 5, 6 and n) 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 (FiG. 4) which results from the first and second 

 divisions. Compare FIG. 5, which shows a tier or series of four 

 cells, with FIG. 4. Then follows (FiG. 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, FIGS. 2-6 with FIGS. 7-10. 

 In each section represented by FIGS. 7 and 9 there is a triangular- 

 shaped apical cell, while in FIGS. 8 and 10 both apical and basal 

 cells of triangular shape are present. FIG. 1 1 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 foo.t. 



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 



