Tg09] SAXTON—WIDDRINGTONIA CUPRESSOIDES 165 
examined in the stages here figured, it seems scarcely possible that 
a second nucleus can be present, but it is unusual for the division 
re - giving rise to the generative and tube nuclei to be delayed so long. 
CoKER (8) reports that this division occurs after shedding in certain 
cases, but says that it occurs before shedding in Callitris sp. As will 
be seen, however, the whole history of the male gametophyte shows 
a minimum of nuclear activity. 
The pollen grain has a fairly thin cellulose endospore and a very 
thick and rather hard exospore (fig. 4), and on germination (as 
shown in the figure) the exospore alone begins to grow, without any 
immediate growth of the endospore or any trace of tube forma- 
tion. The number of pollen grains which begin to germinate in 
each ovule varies from one to four, three being the most usual num- 
ber (fig. 3). The ovule here figured closely resembles that of jig. 1, 
and therefore only a few of the cells have been drawn. 
No trace of a megaspore mother cell or cells can be seen in ovules 
of this age, and stages to illustrate megasporogenesis are unfortunately 
wanting at present. GOEBEL (16) figures an ovule of Tetraclinis 
(Callitris quadrivalvis) in which a considerable number of what 
are probably megaspore mother cells are figured. Several ovules 
considerably older than that just mentioned show the nucellus 
clearly differentiated into peripheral and central regions. This cen- 
tral region and the innermost cells of the peripheral region are 
represented in fig. 5. The cells of the central part are somewhat 
larger and are characterized by having only a very scanty supply of 
cytoplasm. Probably these cells are a large group of megaspores, 
one of which later grows to form the prothallus. In this case GOE- 
BEL’s figure of Tetraclinis would doubtless also serve to illustrate 
the corresponding structure in Widdringtonia. 
It is certain in any case that normally only one megaspore 
develops, since no “secondary prothalli” have been found, as de- 
scribed by Lawson (20) in Sequoia sempervirens. An ovule of 
Callitris verrucosa, however, has been sectioned, which contained 
two secondary prothalli (text fig. 1). In the next stage figured the 
very large prothallus is already formed. The embryo sac 1s lined 
with cytoplasm containing a single layer of free nuclei and bounding 
one large central vacuole. Fig. 6 is a sketch of a whole ovule in 
