4 Eames. — The Morphology of Agathis australis . 
often so far below as to create a stipitate appearance (Figs. 2 and 3). It is 
bounded externally by the above-mentioned layer of larger cells with 
mucilaginous, deeply staining contents. Inwardly is found the megaspore 
membrane. Adjacent to the latter the innermost layers of cells show signs 
of disintegration, and bounding these inwardly are frequently the remains 
of cells absorbed in the development of the gametophyte. The tip of the 
nucellus is at times enlarged, though not greatly, the swelling, perhaps in 
many cases, being limited by the proximity of the micropyle to the cone 
axis, against which the nucellar tissue is frequently firmly pressed. In 
ovules of the age of the vacuolated embryo-sac the nucellar cells largely 
contain starch. This disappears irregularly, for at the time of fertilization 
the upper portions of some nueelli contain much starch, though many have 
none. The presence of this seems to have no effect upon the behaviour of 
the pollen-tube as it passes through. 
Thomson ( 16 ), in a comparative study of the megaspore membrane in 
the Gymnosperms, has shown that the latter in the Araucarians is very poorly 
differentiated structurally. With this statement the writer agrees so far as 
Agathis australis is concerned. In most Conifers this coat becomes thin, 
or is quite lacking at the apex of the gametophyte. Thus the pollen- 
tube is given free access to the archegonia, which are in most cases apical. 
But in A. australis almost reverse conditions prevail : the membrane is not 
thin or lacking below the micropyle, but, on the contrary, its thickness is 
usually increased there to a considerable extent. The regions where the 
membrane is thin or absent lie lower down on the gametophyte. Thus 
a marked cap is formed over the apex of the archegoniate prothallium. 
Fig. 7 shows this thickened terminal portion of the megaspore membrane, 
and suggests also to some extent its function. The tip of the gametophyte 
is shown in longitudinal section with the nucellus, much eroded, surrounding 
it. Portions of the integument are seen on the sides. The very dark line 
externally bounding the nucellus is the epidermis-like layer above mentioned. 
The nucellar tissue is almost entirely destroyed by the pollen-tubes, some 
of the contents of which may be seen on the right. The dark irregular 
lines at the internal boundary of the nucellus are the remains of its de- 
stroyed cells and pollen-tube walls. Lying against these on the inside is 
a homogeneous layer, the megaspore membrane. It is thick above, and 
thins away rapidly in the lower part of the photograph. Its cap-like 
nature is evident. The pollen-tubes have been prevented by its presence 
from destroying the upper portion of the gametophyte. Contrast this 
condition with that in Fig. 9, where the pollen-tubes have broken through, 
as they do at times. Much of the upper section of the gametophyte has 
been eroded. This protective function will be seen below to have a definite 
relation to the position and order of development of the archegonia, as well 
as to the nature of the pollen-tube. 
