12 THE COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
their greatest elongation, mitosis takes place. I shall take the 
opportunity of describing the cytological details in a separate 
paper. For the present purpose it is enough to say that so far as 
my own observation goes four megaspores result from the division 
of each primitive cell. The appearance of the mass of cells which 
results from the division of the archesporial cells is very similar to 
that presented by similar cells arising in the same manner in Heli- 
anthemum Rhodax as described and figured by A. Fischer* accord- 
ing to whom two or three “ mother cells ” are in this form cut off, 
which divide each into four or sometimes six daughter cells (meg- 
aspores) one only of all these resultant cells becoming the mother 
cell of the embryo-sac, the rest suffering disorganization. 
Several or all of the archesporial cells may divide; thus may 
many megaspores arise,among which there is a considerable discrep- 
ency in size (PI. 1, Fig. 9). Of one quartette arising from one mother 
cell, the lowest cell may be the largest; in another, one of the 
middle ones; then again the uppermost may be the largest. I 
have not been able to determine whether there is any constancy in 
the selection of a megaspore to be the mother cell of the embryo- 
sac. The appearance of such material as I have examined seems 
to favor the opinion that any one of them, but more especially 
one of the end cells of the quartette, may be chosen. 
As a rule only oxe of all the megaspores actually germinates. 
Exceptionally in other genera to be hereafter described, I have 
found two embryo-sacs completely formed and lying parallel ; one 
of these usually lies farther forward than the other, and this one is 
functional. 
THE DEVELOPMENT OF THE EMBRYO-sAC 
At the completion of megaspore formation, the chosen mega- 
spore commences a migration along the micropylar canal formed 
as above described by the forward growth of the integument. This 
migratory movement of the functional megaspore appears to be 
unique, for I have not been able thus far to find any reference in the 
literature which shows that such migration has hitherto been ob- 
served. The cap of epidermal cells which overlies 
* Zur Kenntniss der Embry 
Zeitschr. 14: 90. 1880 
the archesporium 
osackentwickelung einiger Angiospermen. Jenaische 
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