232 PICKETT: EMBRYO-SAC OF ARISAEMA TRIPHYLLUM 
carpus foetidus by Rosendahl (6, p. 3). Where more than one 
megaspore mother cell is in a nucellus, division of all the nuclei 
proceeds regularly and may or may not be simultaneous. The 
most nearly simultaneous cases found are shown in FIG. 9, 19, 19d. 
Finally, limited space probably causes a crowding in such cases, 
which results in the checking of activity in some cells and their 
destruction by the growth of others, as suggested by the cells at 
the left in FIG. 15, 15a. 
A few preparations show a cell in a position to indicate its 
origin as a tapetal cell (FIG. 17). Thesame possibility is suggested 
by Gow (5, p. 39-40), in FIG. 6, and is also mentioned by 
Campbell (3, p. 7) for Dieffenbachia Seguine. Such a tapetal 
structure is shown to be well developed normally in Symplocarpus | 
foetidus by Rosendahl (6, p. 2, pl. 1. f. 4 and pl. 3. f. 31). The 
finding of but one such cell showing disorganization as the mega- 
spores develop seems ‘to the writer sufficient evidence to justify 
the conclusion that the formation of a functional tapetum in 
Arisaema triphyllum is unusual or even questionable. 
As has been stated above, during the enlargement and divisions 
of the megaspore mother cells, the outer cells of the nucellus 
undergo periclinal divisions until the sporogenous cells appear quite 
deeply seated. During the same time the nucellar cells become 
well filled with starch (FIG. 15 and 17). Asa result of the later 
gametophyte growth, the lateral portion of the nucellus with its 
contained food material is consumed, so that the mature embryo- 
sac is in contact with the inner integument, except at the apex, 
where a cap of nucellar cells persists (FIG. 20 and 21). The 
temporary storage of food where it is so readily available for use 
by the growing embryo-sac may account for the rapid develop- 
ment of the latter as given below. 
THE EMBRYO-SAC 
One of the megaspores develops into the embryo-sac at the 
expense of the others and of the nucellar tissue. Three nuclear 
divisions occur in rapid succession as in Symplocarpus foetidus 
(6, p. 3). The short time required for these divisions is indicated 
by the fact that out of many preparations of material gathered 
at one time, and showing about this stage, but very few show 
