587 
Life-history of Tetraclinis articulato . 
the ovule when nearly ready for pollination (Figs. 31 and 59) bears a 
considerable resemblance to that of other Cupressoideae. There is a long 
and widely open micropyle, of which the inner cells are quite distinct from 
the rest as the micropyle closing cells. At the apex of the nucellus a few 
cells have begun to collapse, a phenomenon which becomes more notice- 
able after pollination, and which apparently facilitates the penetration of 
the pollen-tube. According to Tison ( 55 ), however, the destruction of the 
apical cells is primarily brought about in the formation of the ‘pollination 
drop \ He remarks : ‘ Cette production de la gouttelette est accom- 
pagnee de la destruction des cellules nucellaires productrices 5 ; this, 
it may be pointed out, is not the case in the CallitroTdeae, where the 
‘ gouttelettes / have been seen in Actinostrobus and W iddringtonia (Saxton 
( 47 )), since in that sub-family the cells at the apex of the nucellus 
remain intact (except where broken down by an advancing pollen-tube). 
This would appear to constitute another distinction, though probably 
not one of any great importance, between Callitroideae and Cupressoideae ; 
the observations relative to this point in the Cupressoideae (Tison ( 55 ), 
Miyake ( 32 ), Nichols ( 36 )) suggest a probability that the formation of 
a saucer-shaped depression at the apex of the nucellus will be found to 
be characteristic of all the genera. 
At the base of the nucellus is a group of sporogenous cells (shown 
on a larger scale in Fig. 32), of which about eight to twelve may be seen 
in median section (either longitudinal or transverse). At this time 
there is not a very sharp boundary line between sporogenous and 
non-sporogenous tissue, but at a somewhat later stage the differentiation 
is more marked (see Fig. 36). The cells of this sporogenous tissue are 
those figured as such by Goebel ( 18 ), and it is quite clear that one of 
their number is the functional megaspore mother-cell, while the remainder 
are also morphologically spore mother-cells, which function as a tapetum 
(spongy tissue). 
Fig. 33 shows the apex of the nucellus, in an average ovule, at about 
the time of pollination. The apical depression is evidently formed by the 
breaking down of certain cells, and is similar to, but perhaps a trifle deeper 
than, that usually found in Cupressoideae. Fig. 34 shows in outline the 
apex of another nucellus with a very similar depression, and, above, the 
micropyle completely closed by the ingrowth of the innermost cells of 
the integument in that region. Thus a sub-spherical and completely enclosed 
cavity is formed in which conditions are doubtless very suitable for the 
germination of the pollen-grain. A transverse section of the closed 
micropyle is shown in Fig. 35. 
For a short time before dividing the functional mother-cell becomes 
distinguishable from its neighbours, as shown in Fig. 36, by the greater size 
of both cell and nucleus. A few starch grains can also be seen in the rather 
