166 BOTANICAL GAZETTE [SEPTEMBER 
optical section at this stage, showing the winged integument (the 
wings are only one cell thick), nucellus, and prothallus. The long — 
tubular micropyle is now very noticeable. The ovules are nearly 
allcurved like this one, so that there is only 
one plane of symmetry in the ovule. Oc- 
casionally a second curvature is found at 
right angles to this one, in which case longi- 
tudinal sections are apt to be puzzling unless 
a whole series is carefully studied. Cones 
containing ovules of about the age shown 
in fig. 6 are growing on the middle branch 
in the accompanying photograph (text jig. 2). 
Those on the right have just been pollinated 
and those on the left have young embryos, 
- all being gathered February 28, 1909. 
Fig. 7 shows the apex of a nucellus 
about the same age as that in fig. 6. Bot 
preparations indicate that only a single pollen 
tube is present and a case is only rarely met 
with in which more than one pollen tube 
develops; though, as seen above, three usually 
begin to germinate. Only two very small 
nuclei are found in the pollen tube of this 
Fic. 1.—Median longi- age, no doubt the tube and _ generative 
tudinal section“of nucellus . 
n, of Callitris verrucosa: it, nuclei. f 
pollen tube; pr‘, primary Fig. 8 represents a very small part © 
prothallus; pr, prs,!second- the prothallus with its lining layer of cy! 
ary prothalli, X40, plasm and two of the free nuclei. In some 
preparations, such as the one figured, the nuclei can be seen t0 be 
paired, probably indicating that a simultaneous division has recently 
taken place. None of these divisions have been seen, but if, a5 § 
probable, they occur always very rapidly and simultaneously there 
might be only about ten separate periods of an hour or two each, 
extending over three months or more, during which the requisite 
stages could be obtained. It may also be that the time of day oe 
night at which these divisions occur is always about the same, though 
there is no evidence that this is so with other divisions; at any 
