Embryo of Sequoia semper virens . 23 
to a comparatively small narrow area in the upper half of the 
prothallium. 
The final division of all the free nuclei which immediately precedes the 
formation of the cellular endosperm is almost simultaneous. The spindle- 
fibrils which connect the daughter-nuclei in this division persist and increase 
in numbers, so that each nucleus is surrounded by a system of delicate 
radiating kinoplasmic fibrils. These fibrils not only connect with the 
sister-nuclei but reach out and join the fibrils of the neighbouring nuclei. 
The result is that large numbers of nuclei become joined together by 
radiating systems of kinoplasmic fibrils. The cell-plates are formed in the 
usual way between the nuclei. The formation of the endosperm in Sequoia 
sempervirens therefore does not follow the method described by Sokolowa 
(1891) for other Coniferales. 
As the vacuole in the upper region disappears, the cells in this region 
are very large and elongated, and these structures are no doubt the 
‘ Alveolen ’ described by Arnoldi. The archegonia are, however, not con- 
fined to this tissue in the prothallium. 
During the development of the primary prothallium one or two 
secondary prothallia advance much more slowly. Their growth is confined 
to the narrow limits left by the primary prothallium. Their form is there- 
fore very irregular, and they never develop cellular tissue. The cells of 
the primary prothallium which are in contact with the protoplasm of the 
secondary prothallia act as absorbing organs. This absorption of the 
protoplasmic substance of the secondary prothallium by the cells of the pri- 
mary prothallium no doubt retards the development of the former and 
prevents it from forming tissue. 
Soon after the endosperm is formed, certain cells deep within the 
upper portion of the prothallium become differentiated into archegonial 
initials. When quite small the primary neck-cell is cut off, and the central 
cell enlarges rapidly and carries the primary neck-cell forward towards 
a pollen-tube. During the enlargement of the central cell the primary neck- 
cell divides once. Occasionally four neck-cells were formed in the arche- 
gonium, but two seemed to be the typical number. Just before the 
archegonium has reached its full size the central nucleus evidently divides, 
for we now have two large nuclei present. These nuclei are of equal size, 
and are situated at opposite ends of the archegonium. The one near the 
neck represents the ventral canal-cell, and the lower one is the egg-nucleus. 
The ventral canal- nucleus very soon becomes disorganized and disappears 
entirely. The lower portion of the archegonium develops a large vacuole, 
and at the time of fertilization the egg-nucleus is centrally situated. As 
the archegonia develop, their elongation is always directed towards a 
pollen-tube, so that each tube becomes partially surrounded by the necks 
of several archegonia. 
