412 Lawson .— The Gametophytes and 
This postponement of the development of the gametophytes, and con¬ 
sequent delay of fertilization for twelve months, occurs in a number of other 
Coniferales, but is evidently not peculiar to any particular family. We have 
it occurring, for instance, in Cephalotaxus (Lawson, ’07 ; Coker, ’ 07 ), Torreya 
(Coulter and Land, ’ 05 ), Pinns (Coulter and Chamberlain, ’01 ; Ferguson, 
* 04 ), and in Sciadopitys. Why this delay should occur in these few genera 
is hard to explain. The habit may be a special adaptation to meet special 
conditions of nutrition ; on the other hand, it may possibly represent the 
vestige of a habit of a resting period of the spores at a very early period in 
the phylogeny of the group when the spores were free. In support of this 
view, however, there is at present no evidence. 
In Sciadopitys no further nuclear changes occur in either the pollen- 
tube or megaspore until the following spring. Early in March of the 
second year, however, the nucleus of the megaspore divides, and this is 
immediately followed by a large number of free nuclear divisions. The 
formation of prothallial tissue now proceeds in the usual way. The free 
nuclei are parietally placed, and after the last simultaneous division, cell- 
walls are formed between them. There are thus formed the primary pro¬ 
thallial cells which are open on the inside and exposed to the central 
vacuole. These structures have been sufficiently described and figured for 
other Coniferales (Coulter and Chamberlain, ’01; Ferguson, ’ 04 ; Coker, 
’ 03 ; Lawson, ’ 04 , ’ 07 , ’ 09 ) since their first discovery by Mile Sokolowa 
in 1890. 
The primary cells now rapidly elongate and encroach upon the central 
vacuole after the manner already described for the Abietineae, Cupressineae, 
and other families. Cross-walls are now formed, and a considerable amount 
of cellular prothallial tissue is produced before the ingrowing cells meet in the 
middle and occupy the space of the central vacuole. 
During the organization of the prothallial tissue there is developed 
a distinct and thick megaspore membrane. Its structure is very like that 
of Pinus , but not quite so thick. It has a distinct fibrillar exospore, and 
is uniformly thick except in the region of the archegonium, where it tapers 
out and becomes quite thin. A sectional view of a part of the membrane 
is shown in Fig. 39. (See Thomson, 1904.) 
The Archegonia. 
The archegonia originate as superficial cells, and make their appearance 
early in April at the apex of the prothallium before the permanent tissue 
of the latter has been completely organized. The original initial cell was 
not positively identified ; probably on account of its similarity to the 
ordinary prothallial cells. The first stage observed was after the first 
division of the initial cell, showing a single neck-cell and a somewhat larger 
cell below, which develops into the central cell. In Fig. 40 is represented 
