34 Gibbs, — Notes on the Development and Structure of 
portion of the nucellus. In this species the wall is much thinner, and the 
granular remains of contents are not so apparent ; the tubes are therefore 
more difficult to see except in section, and the usual twist formed on the 
entrance to the embryo-sac is replaced by a slight swelling of the tube 
(Fig. 9,/. t). 
Endosperm. After fertilization, as the oospore surrounds itself with 
a cell-wall, the definitive nucleus elongates and prepares to divide (Fig. 9, 
d. 7i.). This division, which never takes place before the first segmentation 
of the fertilized egg, is extremely rapid ; amongst all the material examined 
not a single case of actual primary division was seen. 
In preparations, however, showing the first division of the oospore, 
seven or eight endosperm-nuclei have been counted in a series of sections 
through the embryo-sac, and this was found to be the average number for 
this stage. These nuclei migrate at once to the periphery of the embryo- 
sac, where they lie embedded in the cytoplasm, merely dividing to keep 
pace with growth. At the micropylar and chalazal ends of the embryo- 
sac more rapid divisions occur, leading to aggregations of nuclei and a 
denser mass of cytoplasm at each extremity of the sac (Fig. 14, end. c. ; 
Fig. 16, e.s.). 
It has been shown (p. 32) that up to fertilization (Figs. 6 and 7) the 
uniform solution of the layers of nucellar tissue immediately in contact 
with the periphery of the embryo-sac points to its cytoplasm as being 
the digestive agency. This digestion after fertilization receives a definite 
impetus by the aggregation of endosperm-nuclei at the antipodal end of the 
sac (Fig. 16, e. ^.), which elongates rapidly at the expense of the axile rows 
of the nucellar tissue situated immediately below the antipodals (Figs. 18, 
19, ax. c.) until the wall of the embryo-sac arrives in proximity to the 
chalaza, where it enlarges somewhat (Fig. 19, e. j.). 
A comparison of Fig. 7, in which the embryo-sac is fairly vertical and 
is exercising a destructive influence on the cells over its entire periphery, 
with Fig. 19, shows that some definite stimulus must have caused so distinct 
a line to be taken by one particular portion of an organ, and this fact is to 
be correlated with the aggregation of endosperm-nuclei at the chalazal end 
of the embryo-sac. 
As will be shown later, there is reason to suppose that certain layers 
of cells at the base of the nucellus are specialized in a form which suggests 
a tissue for the passage of air and water. 
Ejidosperm cap. Very active divisions of the endosperm-nuclei at 
the micropylar end of the embryo-sac result in an aggregation of nuclei, 
embedded in dense cytoplasm, in the vicinity of the basal suspensor cell, 
thus forming a cap surrounding it (Fig. 14, end. c.). 
At about the time at which the cotyledons are first differentiated these 
endosperm-nuclei arrange themselves peripherally (Fig. 19, end. c.) } free 
