20 ARISAEMA TRIPHYLLUM 
and towards the center. A cylindrical portion immediately be- 
low the embryo is the last to befilled. The cells about the em- 
bryo lose their starch to the growing embryo and remain as a 
mass of crushed cell walls. 
The characteristic feature of Arisaema among the aroids is 
the segregation and the sterility of one daughter of the primary 
endosperm nucleus and the migration of the active endosperm 
nuclei to the micropylar portion of the embryo-sac cavity. The 
formation of a few free nuclei followed by the formation of walls 
simultaneously between these occurs in Lysichiton kamtschatcense 
(4), but in that case the walls extend entirely across the cavity 
instead of breaking it up into irregular cells; and the whole cavity 
is divided up by these cross walls instead of a rather small micro- 
pylar portion as in Arisaema. ‘The formation and persistence for 
a time of large endosperm cells in the micropylar extremity of the 
cavity has been noted in Lysichiton (4) and in Aglaonema com- 
mutatum (6). Along with the other forms, there is in Arisaema 
no migration of the free endosperm nuclei to the peripheral layer 
of protoplasm. 
THE RESIDUAL CAVITY 
As noted elsewhere the formation of endosperm in the upper 
portion of the embryo-sac leaves in the basal portion a large cavity, 
which may be designated as the residual cell or cavity (PLATE 2, FIG. 
31). This cavity contains a lining layer of protoplasm, abundant 
cell sap and a daughter of the primary endosperm nucleus. The 
nucleus is the most conspicuous feature of the cavity, having the 
appearance of a large resting vegetative nucleus with a well defined 
nuclear membrane and a conspicuous nucleolus within the vacuo- 
late nuclear sap (PLATE 2, FIG. 32). Before definite marks of de- 
composition appear, this nucleus may reach a diameter of 100-110 
microns, and its nucleolus a diameter of 20-25 microns. Later 
the nucleolus divides or fragments first into a few and then into 
many small portions. Soon the nuclear cavity shows a more 
marked network of fine threads and by the time the endosperm 
has reached half its mature mass, the outline of the greatly enlarged 
nucleus becomes irregular, the nucleolar fragments disappear and 
only a mass of fine fibrils remain in the cavity. The enlargement 
and disintegration continue as the seed matures until the nucleus 
jaar Ere See os 
