330 Saxton . — Contributions to the Life-history of 
whether any investigator of Conifer morphology has ever tested the value 
of collections made during the night, but it is undeniable that certain stages 
are repeatedly met with in day collections, while others are extremely rare. 
The current explanation, that the rare stages are those passed through very 
quickly, is no doubt true in some cases, but where a single collection includes 
an approximately equal number of stages before and after the one looked 
for, which still is persistently absent, it is not unreasonable to infer that it 
may only occur at a certain time of the day or night other than that at 
which the collection was made, or at least far more frequently at such 
a time. 
The mature archegonia are always found (in normal prothalli) in 
lateral groups of about twenty-five to thirty, abutting on the lower part 
of a pollen-tube, one such group being formed in relation to each pollen- 
tube. It is not always quite clear whether the pollen-tube is actually 
within the tissue of the prothallus, but it is certainly so in many cases, and 
where not apparent may be due to the crushing of the outer cells. Thus 
it is probable that archegonia are always deep-seated, and certain that they 
usually are. Part of a tangential section of a prothallus cutting a single 
group of archegonia transversely is shown in Fig. 15. The microphotograph 
reproduced in PL XXVIII, Fig. 53 shows a similar section. 
The archegonia which may be eventually found in prothalli in which 
no normal pollen-tubes occur, vary a good deal, but a typical case is 
shown in Fig. 1 6, the cells in which contents are drawn being quite sharply 
differentiated from the rest. 
Some other points in connexion with the older ovule and prothallus 
may now be mentioned, although some are only to be observed subsequently 
to fertilization. 
Alternating with the three wings of the integument are found three 
large secretory cavities in the tissue, which may be about 3 mm. long, 
1 mm. wide, and o-i mm. thick. Their position in transverse section is 
indicated in Fig. 17, and one of them is drawn on a larger scale in P'ig. 18. 
It is very probable that resin is secreted in these cavities, but having only 
fixed material at my disposal, which has been repeatedly washed in alcohol, 
it has not been possible to determine this point. It is seen in Fig. 17, and 
more clearly in Fig. 19, that the nucellus has also three quite rudimentary 
wings, corresponding in position to those of the integument. The outline 
of the prothallus in cross-section may be sub-triangular (Fig. 19), almost 
circular (Fig. 17), or somewhat elliptical (Fig. 16). 
The megaspore membrane is, from the first, very thin and incon- 
spicuous, but thickens somewhat in a quite old prothallus. Its thickness 
when a good-sized embryo has been formed is indicated in Fig. 20, which 
also shows two of the marginal starch-packed cells. Two cells near the margin, 
one uninucleate the other binucleate, are shown in Fig. 21. Practically all 
