500 BOTANICAL GAZETTE [JUNE 
It is variable in different ovules. In Agathis it is reported (3) that 
the megaspore membrane is thickest over the apex of the game- 
tophyte and gradually thins out toward the archegonia in such 
a way as to allow the fertilization of the lower archegonia first 
and to protect from the pollen tubes the later maturing upper 
archegonia. There does not appear to be any such difference in 
Araucaria, though it is usually the case that the megaspore mem- 
brane disappears along with the band of dead cells in the region of 
the archegonia (fig. 4). 
The time at which the pollen tubes reach the nucellus is subject 
to wide variations. They may do so as early as July or be deferred 
till late in the fall. The time at which they do so does not appear 
to exert any influence on the development of gametophyte or ovule, 
within the limits mentioned. So many tubes commonly reach and 
penetrate the nucellus that it is almost entirely destroyed. They 
usually enter through the tip, composed of large clear cells with 
little protoplasm, but may occasionally pass between the nucellus 
and integument for a very short distance before entering the former. 
In the cases of the large slitlike micropyles, through which the 
nucellus is exposed for a large part of its upper surface, the tubes 
ordinarily, at any rate, enter only through the tip. There do not 
appear to be any special peculiarities in the way the tubes pene- 
trate the nucellus. They go fairly straight to the region of the 
archegonia. Occasionally one branches; a few strike the cap of 
dead cells over the apex of the gametophyte and then commonly 
turn aside. They are surrounded by a layer of dead cells some- 
what like that around the female gametophyte, though it is less 
extensive and less regular. No indications of the breaking down of 
nucellar cells to make way for a pollen tube were observed unless 
the pollen tube was itself present to account for the effects. The 
nucellar cells below the tip commonly contain much starch, which 
largely disappears with the development of the tubes. 
The uniformity with which the tubes enter the tip of the nucel- 
lus, even when a shorter and apparently more available path is 
present, suggests that they are attracted by a chemotactically 
active secretion from the glandular tip. I did not succeed in demon- 
strating such a secretion. There are often considerable quantities 
