Miyake, The development of the gametophytes etc. 
9 
tissue in Taxodium as not sporogenous in nature, bnt as formed 
from the nucellar cells surronnding the megaspore mother-cell. 
Miss Ferguson (1904) shares the same view in regard to the 
tapetum in Pinus, and attributes to the tissue the function of 
nourishing and protecting the growing prothaHium. I haye also 
observed that the similar tissue in Ounninghamm originales from 
undifferentiated cells of nucellus immediately surrounding the mega¬ 
spore mother-cell. and am inclined to accept the latter Inter¬ 
pretation. 
The growth of the young prothallium is very slow during 
the first month of its development. Fig. 45 shows the stage 
reached on April 30, and on May 17 it has reached the stage 
shown in fig. 49. Growth then becomes more rapid and at the 
beginning of June, the prothallium which is still only a protoplasmic 
sac with an enormous vacuole surrounded by a cytoplasmic layer 
containing numerous free nuclei, attains to a considerable size 
(figs. 50, 109). Fig. 51 shows a part of the parietal layer of pro- 
toplasm in fig. 50 more highly magnified. Fig. 52 shows the 
surface view of the same. The free nuclear division now ceases 
and walls are developed between the nuclei. The rnanner of the 
wall-formation is shown in figs. 53—55. It seems to occur about 
between June 10 and 15. 
The development of the prothallial tissue in Gymnosperms 
was first carefully investigated by Mlle. Sokolowa (1890) and her 
observations have, in general, been confirmed by most of the later 
investigators. The early stages of the prothallium-formation in 
Cunninghamia agrees on the whole with that described by Mlle. 
Sokolowa. Xo wall is formed on the inner side of the protoplasm 
facing the vacuole as first observed by Mlle. Sokolowa in other 
Conifers. A section, made parallel to the inner surface of the 
parietal layer of protoplasm, is shown in fig. 55. The cells are 
polygonal in outline and contain some starch-grains. 
According to Mlle. Sokolowa, the first prothallial cells grow 
inward forming long open tubes which extend to the center without 
division; walls are then formed as the inner end of the tubes meet, 
and later on the cells become divided by cross-waHs. A similar 
process of prothalHum-formation was described by Arnoldi (1900) 
in Sequoia and the same was found to be the case with Taxodium 
studied by Coker (1903). Noren’s (1907) observations on Juni¬ 
perus communis agree on the whole withthose of Mlle. Sokolowa. 
Miss Ferguson's description (1904) of the prothallium-for- 
mation of Pinus differs somewhat from those of the above mentioned 
writers. She States that “no cell has ever been observed to extend 
from the circumference to the center of the prothallial cavityT and 
the first prothaHial cells are divided by cross-walls before they 
reach the center of the vacuole. Lawson (1904b) has observed 
a similar thing in the early stages of the prothallium-formation of 
Cryptomerici, although his Statement of the later stages differs 
markedly from that given by any former investigators. My own 
observations on the formation of the prothallial tissue in Cunning- 
