450 BOTANICAL GAZETTE [DECEMBER 
Summary 
1. The archesporium of Epipactis consists of a single hypodermal 
cell, which, without formation of parietals, functions as the mega- 
spore mother cell. 
2. In most cases the megaspore mother cell divides to two 
unequal daughter cells, the chalazal one again dividing to form two 
megaspores. The innermost megaspore then gives rise to the 
embryo sac. 
3. In other cases four megaspores take part in the formation of 
the sac, the walls appearing at the first two divisions of the mega- 
spore mother cell being evanescent. At least one of these walls 
often shows a tendency to persist, which results in a six-nucleate 
type of sac. The same appearance may also result from irregulari- 
ties in the orientation of spindles. 
4. There is some evidence that the embryo sac may at times be 
derived from two megaspores. 
5. che normal mature embryo sac contains an egg, two syner- 
gids, three evanescent antipodal cells, and two polar nuclei which 
fuse. 
6. The usual type of ‘double fertilization” occurs. 
7. The fertilized egg gives rise to an embryo, which, at least in 
the seed, has no suspensor. 
8. The endosperm nucleus, formed by the fusion of one male 
nucleus with the two polar nuclei, disorganizes without dividing. 
9. The variety of methods by which the embryo sac of Epipactis 
is formed may be regarded as a series representing a reduction in 
the number of nuclear divisions occurring between the archesporial 
cell and the formation of the egg. 
1o. The fate of the nuclei in the different courses of develop- 
ment is probably due to some conditions external to them rather 
than to any inherent potentialities. A normal sac would probably 
be produced by any cell subjected to the conditions under which 
a mother cell would produce one. 
11. The sac in its early stages appears to be an equipotential 
system, polarity being connected with its shape, and the part that 
the nuclei are to play with their position. 
12. The polar groups probably do not represent archegonia, 
