438 Ferguson. — The Development of the Egg and 
nature of the cytoplasm renders this nucleus very liable to 
displacement during the early stages in the development of 
the archegonium, yet, in well-fixed material, it is always found 
in its normal position. Hirase (’ 95 ) states that certain 
granules, which appear in the cytoplasm just beneath the 
nucleus of the central cell in Ginkgo , have been derived from 
the nucleus or from its nucleolus ; and Ikeno (’ 98 ) describes 
the nucleus of this cell in Cycas as giving out a granular 
substance during its growth period. No comparable phe- 
nomenon has been observed in connexion with the nucleus 
of this cell in the species of pines which I have studied ; but, 
as above stated, the nucleus quickly reaches its mature size, 
and remains apparently unchanged until the incept of its 
division. 
Very early in the history of the archegonium, the cells 
immediately surrounding it become differentiated from the ad- 
jacent endosperm-cells by their more regular form, the greater 
density of their cytoplasm, and the increase in the size of 
their nuclei. Thus a distinct sheath, consisting as a rule 
of a single layer of cells, is formed about the venter of 
the archegonium. No special attempt has been made to 
count the number of chromosomes in the nuclei of the various 
parts of the sporophyte and gametophyte ; but whenever 
a nucleus was observed in which the chromosomes were 
particularly clear and distinct their number was always noted. 
In such cases twelve chromosomes have invariably been found 
in the nuclei of the sheath-cells. Chamberlain (’ 99 ) has found 
the same number in the corresponding cells of Pinus Laricio. 
The early development of the archegonium, as just de- 
scribed, agrees in the main with that given by Strasburger 
in 1878. 
As the archegonium grows, the prothallium also continues 
to increase in size, several layers of cells being formed above 
the archegonium, except over its neck-cells. Here no pro- 
thallial tissue is laid down, and hence there arises an opening 
in the endosperm leading from the neck-cells to the nucellar 
cap (Figs. 9-12). In the last stages of development, the sides 
