490 BOTANICAL GAZETTE [DECEMBER 
associations (both short grasses), also bunch grass and sand hills mixed (prairie 
grasses). Each of these types is characterized as to general appearance, 
floristic composition, correlated physical factors, effects of disturbing factors, 
variations from the typical association. e relationships and successions of 
the different associations are outlined, primary and secondary successions 
being recognized, though these do not appear to be fundamentally distinct. 
he remainder of the bulletin is concerned with crop production in the light 
of the data obtained, with practical suggestions as to the choice of land and to 
methods of culture.—LauRA GANO. 
Embryo sac of Pandanus.—In 1908, CAMPBELL published a preliminary 
note on the embryo sac of Pandanus, and in 1909 a fuller paper appeared. 
Now a third paper has appeared," based upon material that shows the com- 
pleted structures of the sac. Three species are included (P. Artocarpus, P. 
odoratissimus, and P. coronatus), so that the results may be regarded as fairly 
representative of the genus. 
e primary sporogenous cell (overlaid by several layers of parietal cells) 
divides into a large inner cell and a smaller outer one, the latter dividing again. 
e embryo sac is developed by the innermost cell, which thus represents two 
megaspores. The usual divisions occur to the 4-nucleate stage (a pair of 
nuclei at each pole of the sac). The micropylar pair divides, and there is 
organized a normal egg apparatus and its attendant polar nucleus. Before 
this occurs, however, the two antipodal nuclei initiate a series of free nuclear 
divisions, accompanied later by wall-formation, until finally 64 or more antip- 
odal cells may be formed before fertilization occurs. A variable number of 
antipodal nuclei are free and fuse with the micropylar polar nucleus to form 
a single large endosperm nucleus, or two such endosperm nuclei may be formed 
by the multiple fusions. In the formation of endosperm by the usual stages of 
free nuclear division, wall-formation, and centripetal growth, the author states 
at the “endosperm nuclei diminish in size as division proceeds, and this dimi- 
nution in size is accompanied by a corresponding reduction in the number of 
chromosomes,” although no count seems to have been made. 
The excessive amount of antipodal tissue preceding fertilization certainly 
suggests that the antipodal cells are to be regarded as representing the vege- 
tative tissue of the gametophyte, and so far as this feature is concerned, it 
seems safe to assume that it is primitive. In the organization of the egg- 
apparatus, however, it is not so much a question of the number of cells in the 
sac at the time of fertilization, as the number of divisions between the mega- 
spore nucleus and the egg. In this case, since two megaspore nuclei are in- 
volved, there are just two successive divisions between a megaspore nucleus 
and the egg derived from it, instead of the usual three divisions.—J. M. C. 
%® Bot. Gaz. 47:485. 1900. 
* CaMPBELL, D. H., The embryo sac of Pandanus. Ann. Botany 25:773-789- 
bls. 59, 60. figs.-2. 1911. 
