Bcrridgc and Sunday. 
167 
OOGENESIS AND EMBRYOGENY IN EPHEDRA 
DISTACHYA. 
BY 
Emily M. Berridge, F.L.S. and Elizabeth Sanday, B.Sc. 
(Concluded from p. 134). 
[Plates II. and III. accompanying this Paper were issued 
with the May Number.] 
Development of Jacket Cells and Abnormal Embryogeny. 
N a large number of ovules, however, this normal method of 
embryogeny appears to be superseded by another in which the 
jacket cells of the archegonium play a leading part. It may be well 
here to review the whole history of these cells from their first 
appearance simultaneously with the archegonium initials, since 
considerable attention has been devoted to them lately in work on 
other groups among the Gymnosperms. 
The common origin of these cells and of the archegonium 
initials from a group of tubular alveoli in the apex of the embryo-sac 
has been mentioned before. At the time when the primary neck 
cells are being cut off from the initials, the tubular cells between 
the latter are undergoing a series of divisions and forming rows of 
jacket cells arranged in a regular manner. The likeness of these 
to the central cells, except in the matter of size, is apparent in 
Fig. 4. Such a similarity of origin and appearance in Sequoia 
sempervirens , has led Professor A. A. Lawson to the view that the 
jacket cells are sterile archegonium initials (9). 
This tissue keeps pace with the growth of the central cell first 
by cell division, and later by individual growth of the cells. They 
soon become crowded with food material, and the nucleus divides 
into two by direct division long before this occurs in the central 
cells. Sometimes three nuclei are found in one cell, but the third 
is usually small or incompletely cut off. Strasburger, after 
describing this mode of direct division in the jacket cells of Ephedra 
alte briefly remarks that it is followed by division of the whole cell. 
This does not seem to be the case here, for the number of jacket 
cells does not increase to any extent after the appearance of this 
mode of division. The separation of the two nuclei is frequently 
incomplete, or one of them assumes a dumb-bell shape, which gives 
the impression that division is going on continuously. 
i 
