Cupressineae , with special reference to Libocedrns decurrens . 287 
(Coker, ’ 04 ) or in the Abietineae. All trace of this layer of cells becomes 
lost soon after the germination of the functional megaspore. 
It seems that only one of the megaspores germinates ; the others, along 
with the layer of loose cells, are presumably absorbed by the growing 
young prothallium. The functional spore at first increases enormously in 
size, and its growth is accompanied by a rapid and successive free nuclear 
division. PI. XXV, Fig. 12 shows the condition of the spore three weeks after 
the stage represented in PL XXIV, Fig. 11. The megaspore as shown in 
Fig. 1 2 contains several large vacuoles separated from each other by irregular 
strands of cytoplasm, and in the cytoplasm are numerous free nuclei in various 
stages of mitosis. At this stage a very distinct but very thin megaspore mem- 
brane was observed. With the further increase in the size of the megaspore 
or young prothallium the vacuoles within it also increase and eventually flow 
together. From a study of these early stages in Libocedrus and many 
other Conifers it would seem that the large central vacuole, which is always 
present, performs a most important function in the growth of the young 
prothallium. The megaspore being confined within the sporangium, the 
young prothallium finds itself completely surrounded by nucellar tissue. 
Therefore, in order to rapidly produce prothallial tissue, it must not only 
increase greatly in size, but a rapid and plentiful supply of food material is 
necessary. Both of these objects must be accomplished by a pressure from 
within. The vacuole always keeps the parietal layer of cytoplasm at the peri- 
phery of the spore in close touch with the surrounding cells of the nucellus, 
and owing to the osmotic pressure which such conditions must necessarily 
bring about, the food substances from the surrounding tissue may be readily 
absorbed. 
The manner in which the nucellar tissue of the prothallium becomes 
organized is not unlike that found in many other Conifers. By the first week 
in May the central vacuole has reached an enormous size, but as yet there 
is no trace of cellular tissue having been formed. Fig. 13 represents a 
section of the lower half of the prothallium at this time. Here the thin 
parietal layer of cytoplasm may be seen lining the spore membrane, and in it 
numerous free nuclei lie embedded at more or less regular intervals. The great 
size of the vacuole may be readily seen by comparing it with the size of the 
nuclei. The parietal layer of cytoplasm is a mere film ; as shown in Fig. 14 
it is quite as thin as the diameter of the nucleus. Very soon after the stage 
represented in Fig. 13 the parietal layer increases to twice or three times its 
original thickness, and meantime free nuclear division has progressed and 
the nuclei lie much closer together. The last mitosis of the free nuclei 
results in the formation of cell-walls. These walls, however, only separate 
the nuclei from one another, the resulting primary cells being exposed on 
the inner side to the sap of the vacuole in the manner first described by 
Sokolowa (’ 90 ) for other Conifers. By their growth inward these primary 
