*5 
Embryo of Sequoia semper virens. 
prothallium. In cross-sections of this region, as shown in Fig. 26, they may 
be easily distinguished from the surrounding vegetative cells. When first 
differentiated, their distinguishing characters are their large size, highly 
granular cytoplasm, which stains readily with orange G., and each one has 
a large, centrally situated, deeply staining nucleus. When first distinguish- 
able, the archegonial initials are not much larger than the ordinary vegeta- 
tive cells by which they are surrounded. They rapidly increase in size, 
however, and are soon several times their original dimensions. As they do 
not all enlarge simultaneously, they present various shapes and sizes, and 
sections very frequently showed the matured archegonia and the young 
initials in the same plane. As the initial grows in size, the cytoplasm 
appears more conspicuously granular, and the nucleus becomes much larger 
as it prepares for the division which cuts off the primary neck-cell. This 
first mitosis of the archegonial initial takes place during the latter part of 
June. Sections of material collected June 25 showed an abundance of the 
various stages of the spindle. Fig. 20 shows one of them with the chromo- 
somes on the way to the poles. These various stages of mitosis afforded an 
excellent opportunity of confirming the observation made during the endo- 
sperm-formation, that the number of chromosomes in the gametophyte is 
half that of the sporophyte. A comparison of Fig. 20, which represents the 
last spindle but one in the life-history of the gametophyte, with Fig. 32, 
which represents the first mitosis in the history of the sporophyte, shows 
without much question the difference in the number of the chromosomes in 
the two generations. 
In addition to the archegonial initials numerous jacket-cells are also 
differentiated. These are distributed very irregularly among the arche- 
gonia. Some archegonia may be almost surrounded by the jacket-cells, 
while others may be completely devoid of them. In the early stages of 
differentiation it is impossible to distinguish between the jacket-cells and 
the archegonial initials. They are structurally identical in regard to their 
cytoplasm and nuclei. This fact, accompanied with their irregular distribu- 
tion over the prothallium, suggests very strongly that the jacket-cells are 
archegonial initials which have become sterile. 
As soon as the first mitosis is completed, the archegonial initial is 
divided into two by a distinct cell-wall. The two cells thus formed are the 
central cell and the primary neck-cell. The central cell now grows very 
rapidly, and, as shown in Fig. 21, comes to be many times the size of the 
primary neck-cell. It was noticeable that the elongation of the central cell 
always took place in the direction of the neck-cell, so that the latter was 
forced forward toward the periphery of the prothallium. As it is pushed 
forward by the elongation of the central cell, the neck-cell divides, so that 
before it reaches the periphery of the prothallium the archegonium has two 
distinct neck-cells. It may be mentioned that Shaw (1895) reported the 
