462 WoopBURN: EMBRYOLOGY OF REBOULIA HEMISPHERICA 
reaching the egg the sperm nucleus is found to have the form and 
structure of a nucleus in the resting stage (Fic. 1). Quite similar 
conditions have been reported by Black (1) and Garber (3) for 
Riccia and by K. Meyer (4) for Corsinia. The form and structure 
of the egg and sperm nuclei at this stage are to a certain extent 
similar (Fic. 1). The egg nucleus is larger and shows a coarser 
and more open disposition of the chromatin. An unstained area 
surrounds the nucleolus. A smaller nucleolus is present in the 
sperm nucleus. The latter as a whole stains somewhat more 
heavily than does the nucleus of the egg. 
The accompanying figures are drawn as nearly as possible in 
that position which is occupied in nature. For instance, the 
necks of the archegonia at this stage of development project obli- 
quely downward or toward the substratum. Consequently it 
will be seen that, in Fic. 1, the sperm nucleus lies in contact with 
that side of the egg nucleus which is toward the neck of the 
archegonium. The membrane of the egg nucleus is somewhat 
infolded along the surface of contact. 
Compared with corresponding stages in the life history of 
gymnosperms and angiosperms we know very little concerning 
the details of nuclear behavior in this and further stages of fer- 
tilization. 
EARLY DIVISIONS OF THE EMBRYO 
The first division wall of the zygote is laid down transversely. 
Fic, 2 represents the telophase of this first division, with the cell 
plate in the process of formation. The spindle lies parallel with 
the longitudinal axis of the venter of the archegonium; conse- 
quently a transverse basal wall results (Fics. 2 and 3). In 
Fic. 3 the nuclei are in the prophase of subsequent division; 
‘‘a”’ represents the hypobasal cell or that one next tothe base of 
the archegonium, and b, the epibasal cell or that one next to 
the neck of the archegonium. The second division is transverse 
and occurs in the epibasal cell (compare Frcs. 3, 4, 5 and 6). 
The epibasal cell (Fic. 3, “‘b”’), with the chromosomes clearly dif- . 
ferentiated, is ina more advanced stage of prophase than the hypo- 
basal cell. There is also evidence of centrosomes or centrosome- 
like structures connected with the nucleus. Fic. 4 represents 
the second division completed. Later stages (compare FiGs- 

