4 
Sa 
a 
4 
‘ 
1909] BROW N—EMBRYO SAC OF HABENARIA 245 
several other orchids (WARD ’80, STRASBURGER ’84), which have 
only three megaspores. 
In Cypripedium (PAcr ’08) the daughter cells of the megaspore 
mother cell do not divide, but one of them forms the embryo sac. In 
this case the question arises as to whether the division of both daughter 
cells has been omitted, in the way indicated for one of them in Habe- 
naria, and the place of the second “reducing division” changed to the 
embryo sac mother cell (the cell within the walls of which the embryo 
sac is organized); or whether the first two nuclei of the embryo sac 
are, as Miss Pacer calls them, megaspore nuclei. In favor of the latter 
view it may be said that the “completion of chromosome reduction” 
which takes place in the division of the daughter cell is necessary to 
the normal development of the embryo sac. COULTER (’08) thinks 
that because chromosome reduction, which is usually associated with 
megaspore formation, is necessary that megaspore nuclei cannot be 
omitted. On the other hand, the place of reduction is not always 
constant, even in nearly related plants, as in the case of Nemalion 
(WoLFE ’04) and Polysiphonia (YAMANOUCHI 705). In Nemalion 
the fertilized egg divides to carpospores and, according to WOLFE, 
reduction takes place in their formation. In Polysiphonia reduction 
does not take place in carpospore formation, but the carpospore oe 
minates to a plant with the diploid number of chromosomes. This 
plant bears not carpospores but tetraspores, and reduction takes place 
in the division of the tetraspore mother cell. In speaking of Poly- 
siphonia, Yamanoucut says: “The tetrasporic plants may have arisen 
by a suppression of the reduction phenomena in connection with the 
Carpospore, so that it germinates with the sporophytic number of chro- 
Mosomes. . . . . The period of chromosome reduction would be 
thus postponed from the carpospore to a later period in connection 
with the newly formed plant.” If, as seems probable, the place of 
reduction has been changed among the red algae, it is reasonable to 
Suppose that it may also have been changed in some angiosperms, and 
“specially if the structure in which it normally occurred had been left out 
of the life-history of the plant. The leaving-out of the division of the 
the mother cell into megaspores would simply be the completion of a 
tendency toward the reduction in the number of divisions of the arche- 
Sporial cells from the condition in the ferns (where it divides a number 
