Embryo of Sequoia sempervirens. 1 1 
and since (as we shall point out later) they have a considerable influence 
on the ultimate form of the primary prothallium, we will designate them as 
the secondary prothallia. 
The growth of the primary and secondary prothallia is always accom- 
panied by a rapid division of their free nuclei. Stages were found showing 
two, four, eight, sixteen, and thirty-two free nuclei. It was too difficult to 
count the numbers greater than this in sections, but this was sufficient 
to indicate that there is a regular and successive division of all the free 
nuclei, at least in these early stages. By the time the prothallia have 
reached the two or four nuclei stage the sporangium has increased to over 
twice its length. As Shaw (1895) has pointed out, the growth resulting 
from the elongation of the nucellus is very much greater in the region 
between the spores and the chalaza. 
At the time when there are eight or sixteen nuclei in the prothallium, 
as shown in Fig. 12, there is a layer of cytoplasm lining the walls, and there 
may be several vacuoles separated by strands of cytoplasm which contain 
many starch-granules. The nuclei at this time are suspended in a broad 
strand of cytoplasm which runs the length of the young prothallium and 
are usually arranged in a row, as shown in Fig. 12. 
The further increase in the size of the primary prothallium is always 
accompanied by an increase in the size of the vacuoles as well as an increase 
in the number of free nuclei. Although the primary prothallium is at this 
time somewhat larger than the secondary, the two present much the same 
condition. From now on, however, the rate of their development is very 
different. The development of the primary prothallium proceeds very 
rapidly, and is followed very slowly by that of the secondary, which, as we 
shall see later, never produces true cellular prothallial tissue. 
The initial stages in the development of the prothallium agree in 
general with the conditions found in Taxus by Jager (1899) and Campbell 
(1902), and in Pinus by Coulter and Chamberlain (1901), with this 
difference, that more than one prothallium in Sequoia reaches an advanced 
stage of development The following events, however, which lead to the 
formation of the cellular prothallium differ in many interesting respects 
from any of the Conifers in which the endosperm-formation has been 
worked out. As Arnoldi (1899-1900) has pointed out, the events are 
strikingly similar to those found by Lotsy (1899) in the formation of the 
endosperm in Gnetum. 
As the vacuoles in the primary prothallium grow, they eventually fuse 
together to form an enormous single vacuole which forces the cytoplasm 
and the nuclei to the walls. As represented in Fig. 13, the prothallium now 
consists of a large central vacuole, surrounded by a comparatively thin layer 
of cytoplasm in which a large number of free nuclei are distributed along 
the wall which surrounds the whole structure. The amount of cytoplasm 
