1892,] Botany. 955 
this sac consists of but a single nucleated cell, which, when division is 
complete, forms a central row of cells. The nucellus in process of 
growth becomes very much elongated; its cells are well defined and 
nucleated ; likewise the mother-cell of the embryo-sac, though primi- 
tively polyhedral in outline, but later more oval in contour, elongates 
and contains a nucleus with nucleolus, imbedded in a rich mass of 
protoplasm. In some sections the nucleus appeared to be ee 
in the same direction as the embryo-sac. 
During the subsequent growth of the integument and the nucellus, 
the embryonal sac enlarges, and the nucleus of the mother-cell under- 
goes sub-division. In a specimen seen the nucleus had divided, and 
the mother-cell afterward separated into two equal parts by a trans- 
verse wall, each part containing a nucleated cell. Presently the two 
nuclei divide, a transverse wall is formed in each half, and thus we 
have, at the end of the second and last sub-division of the mother-cell 
of the embryo-sac, four equal, nucleated cells. At this stage of the 
embryo-sac there is a very close analogy to the division of the mother- 
cell into four cells worked out by Strasburger in Polygonum and Sen- 
ecio. The cross walls formed between the cells are very strongly 
refractive and much swollen; the middle transverse wall is remark- 
ably distended, and persists much longer than the other two partitions ; 
in several sections the middle wall was found intact when the contents 
of the cells were completely absorbed. Of the four cells into which 
the primitive mother cell of the embryonal sac is now divided only 
the lower one is characterized by further growth; this cell, therefore, 
becomes the true mother-cell of the embryo-sac. Subsequently the 
protoplasm of the upper three cells becomes viscid, the nuclei show dis- 
integration, and the upper wall of the lower, club-shaped cell (mother- 
cell) indicates a rigid turgescence. When the upper three cells begin to 
disorganize (in centrifugal order), they become crescent-shaped, their 
nuclei disappear, their walls are displaced, and the cell contents are 
absorbed by the encroachment of the lower mother-cell. After the 
cells are completely disorganized and absorbed the mother-cell assumes 
a central position in the embryo-sac. 
Simultaneously with the obliteration of the upper cells of the 
embryo-sac the one-cell-layer of the nucellus undergoes a similar pro- 
cess of disintegration. The first mark of displacement is shown by 
the reduction of the cell contents to a granular mass of protoplasm ; 
then follows the disappearance of the transverse cell walls. The order 
of nucellar displacement begins at the apical end of the nucellus and 
proceeds towards its basal portion; finally the whole nucellar tissue is 
