1908] GOW—STUDIES IN ARACEAE 39 
adjacent tissue. When the outer integument has closed over the 
nucellus, the first nuclear division in the embryo sac usually occurs 
(fig. 22). This is followed by the usual divisions (figs. 23, 24, 25), 
until eight nuclei are formed, which assume the usual positions. In 
this case the polar fusion was observed (figs. 24, 25). Before the 
embryo sac is complete, the lateral tissue of the nucellus has usually 
disappeared, only the tissue at the tip remaining. 
FERTILIZATION.—Although the material was at the proper stage 
to show fertilization, good preparations were very difficult to obtain. 
The best are shown in figs. 26, 27, 28, and double fertilization is evident. 
ENDOsPERM.—Before the first division of the fertilized egg takes 
place, the embryo sac has increased greatly in size and has become 
almost completely filled with endosperm. The endosperm begins 
with free nuclear division, which continues until numerous nuclei 
are distributed through the sac. Later wall-formation occurs 
(fig. 28) and the sac is filled with tissue. 
EmBryo.—At the close of the free nuclear stage of the endosperm 
the fertilized egg divides transversely (figs. 29, 30); then longitudinal 
and transverse divisions follow in no definite sequence until the 
spherical proembryo is produced (fig. 28). 
CHROMOSOMES.—The preparations of Dieffenbachia were unusu- 
ally favorable for a definite count of chromosomes, and the alter- 
nating numbers were found to be eight and sixteen. 
3. AGLAONEMA VERSICOLOR 
Flowering material of this East Indian species was also obtained 
from the New York Botanical Gardens. The earlier stages of the 
microsporangium were not found, but quite a complete series was 
obtained showing the development of the megasporangium. 
Microsporancium.—In_ the youngest material examined the 
tapetum and middle wall layers had disappeared, leaving only the 
distinct endothecium overlaid by the epidermis. At this stage the 
mother. cells have rounded off and are forming the tetrads. In 
older material the division into tube and generative nuclei was 
observed and eight chromosomes were counted (the reduced number). 
MEcasPoraNGrum,—Aglaonema has one carpel containing a single 
anatropous ovule, which is cauline, although its lateral position at 
