OE Pe Fie PN eo oe UN RI Oi ee a eri a 
1910] CHAMBERLAIN—DIOON EDULE 419 
evident from the fact that development is weakest in the upper 
portion of the egg. 
The nucleus of the sperm enlarges somewhat during its passage 
to the egg nucleus, but details in the changes in its chromatin and 
changes in the chromatin of the egg nucleus were not studied. 
No preparation was secured which would show whether the chro- 
matin contributions of the conjugating nuclei are distinct, as in 
Pinus, or whether the nuclei fuse in the resting condition, as is 
claimed for some gymnosperms. For a study of the nuclei at 
the time of fusion, Ceratozamia is a more favorable form, and 
consequently this feature will be investigated in that genus. 
Embryogeny 
HISTORICAL 
The development of the cycad embryo has been studied in only 
two genera, Cycas and Zamia, and a few rather later stages have 
been noted in Ceratozamia and Encephalartos. 
As early as 1877 Warminc (1) described some of the later 
Stages in the development of the embryo of Ceratozamia, but in all 
Cases the embryo had already passed through the base of the egg 
and invaded the endosperm. He noted the long suspensor and 
particularly the single cotyledon, a feature which Sister HELEN 
GELA (6) has since proved to be due to gravity, the missing 
cotyledon always appearing when developing seeds are rotated on 
a stat. 
TrEvB’s account of Cycas circinalis (2) in 1884 was compara- 
tively full. A prolonged period of free nuclear division results in 
the formation of numerous free nuclei which are crowded to the 
Periphery by a large central vacuole. Wall-formation then begins 
and the embryo, with its long suspensor, is organized from the 
cells at the base of the proembryo. 
IkENo’s (3) account of Cycas revoluta confirms TREUB’s except 
in regard to the formation of the vacuole. IKeNo finds that a 
large number of small vacuoles appear in the cytoplasm of the 
central portion of the egg, and that this central portion with its 
Contained nuclei then disorganizes, leaving a parietal layer of 
_ Protoplasm and nuclei, while a single large vacuole occupies the 
