566 Saxton.—Contributions to the Life-History of Callitris . 
genera should be kept apart, and has cited the opinions of some other 
botanists both for and against this view, which need not here be repeated. 
The evidence was not brought forward at that time, as it was thought better 
to postpone it until the life-history of Callitris had been more fully 
worked out. 
Table II gives a list of the chief differences noted, including both those 
which are more obvious and those more recondite. Since not all the species 
of either genus have been examined, it may prove that not quite all of the 
differences given will prove constant, but it is highly improbable that many 
of the distinctions will be broken down. 
TABLE II. 
Organ or Stage. 
Widdringtonia. 
Callitris. 
Leaves. 
Opposite and decussate. 
In alternating whorls of three. 
Female cones. 
Two decussate pairs of scales. 
All scales equally fertile. 
Six scales in two alternating 
whorls. Outer scales smaller 
and bearing fewer ovules. 
Ovules. 
Not more than about thirty 
in a cone. Most develop up 
to free nuclear conditions of 
the prothallus (except when 
not pollinated). 
About sixty in a cone. Many 
abort very early and appear 
merely as a flat scale, slightly 
thicker in the middle, and 
eventually of almost the same 
size as the fertile seed, but 
apparently containing no 
nucellus. 
Megaspore mother- 
cells. 
About sixty-four at base of 
nucellus. 
One or very few half-way up 
the nucellus. 
Young 
prothallus. 
Appears in lower half of nucel¬ 
lus. No ‘ pavement tissue ’. 
Appears in upper half of nu¬ 
cellus. * Pavement tissue ’ 
below. 
Mature prothallus. 
Relatively large. 
Relatively small. 
Archegonia. 
More than twenty-five in more 
than one group. 
Less than twenty-five in one 
group. 
Seeds. 
Relatively large. Wings not 
very broad or may be obsolete. 
Relatively small. Wings broad. 
Male cone. 
Sporophylls in decussate pairs. 
Sporophylls in alternating 
whorls of three. 
Microsporophyll. 
Bears four sporangia. 
Bears three sporangia. 
Chromosomes. 
Six and twelve. 
More than six and twelve. 
(Perhaps eight and sixteen). 
Habitat. 
South and Central Africa and 
Madagascar. 
Australasia. 
The anatomy of leaf and stem also shows considerable differences 
between the two genera. An account of this has been published elsewhere 
by the writer ( 15 ). 
