
784 THE AMERICAN NATURALIST.  [Vor. XXXVI. 
Among other similar cases may be mentioned that of the 
peculiar aroid, Lysichiton, which occurs upon the northern shores 
of the Pacific. The original antipodal cells divide in this case also, 
and their nuclei become enormously enlarged (Fig. 4 D). 
From a study of the numerous instances which have been 
studied, it is clear that the antipodal cells are by no means 
merely vestigial structures, but are often of great physiological 
importance, replacing the endosperm to some extent, or acting 
as a medium for the transport of nutriment to the developing 
embryo. 
THE ENDOSPERM. 
In the typical angiosperms the primary endosperm nucleus 
resulting from the fusion of the polar nuclei divides to form 
many free nuclei lying in the peripheral layer of cytoplasm. 
Walls form between these nuclei, and a layer of tissue is thus 
developed, lining the embryo sac. By subsequent centripetal 
divisions the embryo sac becomes finally completely filled 
with endosperm. When the embryo ultimately fills the whole 
embryo sac the cell divisions in the endosperm may be entirely 
suppressed (z.g., Naias). In other cases the first division of 
the primary endosperm nucleus is followed by a cell wall 
extending across the cavity of the embryo sac, which is thus 
filled from the first with tissue. 
A modification of the type has been noted in a number of 
low monocotyledons. Of the two nuclei resulting from the 
division of the primary endosperm nucleus, only the upper one 
divides further. The lower one, which may be separated by a 
wall from the upper part of the embryo sac,! sometimes becomes 
enormously enlarged (Fig. 5 C) but does not divide further. 
It is possible, although this has not been demonstrated, that in 
some cases there is no fusion of the polar nuclei. 
A condition somewhat intermediate between the ordinary 
form and that just described was recently observed by the 
writer in Spathicarpa sagittefolia, a South American aroid. 
In this casé (Fig. 5) a group of a few very large cells, with 
Finis The Life History of Sagittaria variabilis, Botanical Gazette, vol. xxiii, 
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