1911] BROWN & SHARP—EPIPACTIS 443 
The fact that in these cases the wall between the two chalazal 
nuclei is decidedly thicker than those between the micropylar 
nuclei would seem to indicate that it had been formed at the time 
of megaspore formation rather than later by a double spindle as 
described above, for in the latter case the division of the double 
spindle lags behind that of the micropylar ones. It thus appears 
that a six-nucleate sac of this type may originate by either of two 
methods. 
Should the wall formed at the first division of the megaspore 
mother cell persist until after the second division, we should have a 
development similar to that of Smilacina (MCALLISTER 9g), in 
which the walls separating the four megaspores break down, leav- 
ing in a single large cell the four nuclei, which then divide once to 
form an eight-nucleate sac. 
A number of two-nucleate sacs were observed with apparently 
but one degenerating cell present at the micropylar end. Further 
evidence on this point was not obtained, but these may represent 
cases in which the embryo sac is being derived from a daughter 
cell, or, in the light of the above, from two megaspores. 
The development of embryo sacs from two or from four mega- 
spores in a plant, which also forms them from one megaspore in the 
usual manner, may be regarded as steps in the reduction of the 
number of nuclear divisions occurring between the archesporial cell 
and the formation of the egg. When four megaspores take part 
in the formation of an eight-nucleate sac, the egg is removed from 
the archesporial cell by three divisions, as is also the case in Cypri- 
pedium (Pace 11), in which the egg nucleus is one of four formed in 
one daughter cell. Should one more division in any way be elimi- 
nated, the egg nucleus then being one of the four products of the 
reducing divisions, the gametophytic generation would be repre- 
sented by a single nucleus, and the condition would be exactly 
comparable to that of the animal egg. 
The further fate of the embryo sac, whether derived from one, 
two, or four megaspores, is apparently the same. The pollen 
tube makes its way through the micropyle into the sac, disorgan- 
izing one of the synergids, and liberates two male nuclei, one of 
which fuses with that of the egg, and the other with the product 
