Cupressineae , with, special reference to Libocedrus decurrens. 289 
diminishing the central vacuole. The nuclei, during this growth of the 
primary cells, take up their characteristic position, on the inner side ex- 
posed to the vacuole. The final formation of permanent tissue takes place 
in the manner described above for Libocedrus and Taxodium (Coker, ’04). 
In Libocedrus , Thuja, Cupressus , and Chamaecyparis there is a distinct 
but poorly developed megaspore membrane at the time the archegonia are 
formed. An accurate account of the distribution and character of this 
membrane has already been given by Thomson (’05). 
During the development of the central cells the sterile tissue at the 
apex of the prothallium grows forward, leaving the archegonia behind. 
The result of this forward growth is the formation of a large, deep, cup-like 
depression, or archegonial chamber, at the base of which the neck-cells of 
all the archegonia are closely clustered together. It is into this chamber 
that the contents of the various pollen-tubes are eventually discharged. 
While the male cells of the Cupressineae present characters which are 
apparently more primitive than those of the Abietineae, it must be remem- 
bered that their function and form are correlated with this highly specialized 
condition of the grouping of the archegonia. The formation of a common 
archegonial chamber into which the tube contents are discharged makes it 
possible for both male cells to function, and these structures are therefore 
not reduced or dwarfed as is the case with so many other Coniferales. This, 
however, will be discussed more at length under the head of fertilization. 
The Archegonia. 
The archegonia in Libocedrus are always arranged in a single group, 
and vary in number from ten to fifteen. The initials become differentiated 
as a group of cells at the apex of the prothallium as soon as the permanent 
tissue of the latter has been organized. They are all of superficial origin. 
The youngest initials observed were several times larger than the neigh- 
bouring cells, and their nuclei were very conspicuous and stained deeply. 
The further growth of the archegonia is evidently very rapid. The next 
stages observed showed the neck-cells, and these seemed to vary in number 
from four to six, arranged in a single tier, no periclinal walls being formed. 
As soon as the neck-cells have been formed the central cell becomes 
elongated enormously, and the nucleus, which also increases in size, takes up 
a position in the cytoplasm very near the neck. Meantime quite a large 
vacuole makes its appearance in the central region of the archegonium. The 
central nucleus now undergoes division, and this results in the organization of 
the egg-nucleus and the ventral canal-nucleus. All of the central nuclei of a 
single archegonial complex seem to divide nearly simultaneously. One pre- 
paration showed the nuclei of five neighbouring central cells in the spindle 
stage. Other preparations showed these nuclei in various stages of mitosis. 
All of the Cupressineae so far investigated, including Taxodium (Coker, ’04) 
