642 Miyake and Yasui—On the Gametophytes and 
almost level with the base of the archegonia the membrane thins out rather 
abruptly, and from this region to the very apex of the prothallium no trace 
of the membrane could be detected \ In Pseudolarix , as in the majority of 
the Abietineae studied by Thomson, the megaspore membrane is present 
in the micropylar region of the prothallium, where it is much thinner than 
at the basal portion. 
As soon as the female gametophyte is filled with solid prothallial tissue, 
archegonial initials appear at the micropylar end of the prothallium. This 
seems to take place early in June. One of the earliest stages of the young 
archegonia observed is shown in PL XLVIII, Fig. 15. This is figured from 
the material received on June 6. The archegonial initial has already 
divided once, and the primary neck-cell is cut off from the central cell. 
The primary neck-cell is soon divided into two cells by an anticlinal 
wall (F'ig. 16). The two cells then divide again by walls perpendicular to 
the first. The four cells thus formed usually divide once more by periclinal 
walls, and two tiers of four cells each are formed (Fig. 22). These constitute 
what may be called the normal neck of the mature archegonium. In some 
archegonia, however, the neck was found in a longitudinal section to consist 
of two tiers of four cells each, suggesting that there may be eight cells in 
each tier. 
The central cell increases in size quite rapidly, and in about three weeks 
after the formation it reaches the full size. In the early stages of develop¬ 
ment it contains a large vacuole occupying the greater part of the cell 
(Figs. 15, 16). The presence of a similar vacuole has been observed in the 
young archegonia of Tsuga (Murrill ’00), Taxodium (Coker ’ 03 ), Cunning- 
hamia (Miyake TO), Dioon (Chamberlain ’ 06 ), and several Cupressineae 
(Strasburger ’ 79 , Land ’ 02 , Noren ’ 07 , Lawson ’ 07 ), and may probably 
represent the normal condition in the young central cell of the Gymno- 
sperms. The formation of the central vacuole may be considered as a result 
of the growth of a cell without a corresponding increase of its cytoplasm, as 
in the case of the young female gametophyte. Later, the vacuole gradually 
decreases in size, and the cell is gradually filled up with cytoplasm. The 
cytoplasm is at first vacuolate, but later it becomes more dense and granular. 
The nucleus is, from the first, always situated at the apex of the cell just 
beneath the neck (Figs. 15-17). 
Enveloping the central cell is a layer of sheath or jacket cells, which 
are scarcely distinguishable from the adjacent cells of the prothallium in 
the early stage of development (Fig. 15). But later the cytoplasmic 
contents become more dense and the nuclei much larger, and in the mature 
archegonium they are well differentiated (Figs. 22, 23). 
The number of archegonia in a single ovule varies from four to seven, 
the more usual number being five or six. As in other Abietineae the 
archegonia are arranged quite separate from one another, and they may 
