6oo 
Saxton.— Contributions to the 
(Since it is considered that in the present case the phylogeny has followed 
more or less definite geographical lines, the phylogeny and the geographical 
distribution have been indicated together on a sketch-map.) 
The geological and general biological evidence for the former existence 
of a great antarctic continent, providing a land connexion between Southern 
Africa and Southern Australia, is very strong ; the view that the separation 
of Actinostrobus and Callitris from Widdringtonia took place during this 
period would be more or less in agreement with the conclusions reached on 
general grounds as to the antiquity and relationship of these genera. 
Summary. 
A detailed account is given of microsporogenesis in Tetraclinis. 
No fusion of two spiremes occurs at about the time of synapsis. 
The mother-cell does not become partitioned during the development 
of the microspores. 
Approximately three months elapse between pollination and fertiliza- 
tion, and development during that time is continuous. From the first 
appearance of the strobili to the complete ripening of the seeds takes about 
twelve months. 
The mature pollen-grain is uninucleate. 
The ovule closely resembles that of other Cupressoideae, and has 
a single functional megaspore mother-cell, surrounded by tapetal tissue. 
The possibility is suggested that all the Cupressoideae conform to this type, 
errors of interpretation accounting for descriptions of a quite different 
structure in two genera. 
The development of both gametophytes is quite like that of other 
typical Cupressoideae. 
The occasional occurrence of lateral archegonia is an interesting feature. 
In fertilization the male nucleus is about one-quarter of the size of the 
female. 
Complete fusion of the male and female nuclei occurs while both are in 
the resting stage. 
In the prophases of the first sporophyte division a segregation of the 
chromosomes into two groups occurs (presumably male and female). This 
is regarded as important evidence of the continued individuality of male 
and female chromosomes. 
Wall-formation in the proembryo apparently occurs in the transition 
from the four-nucleate to the eight-nucleate condition. 
The mature proembryo is somewhat variable in the number and 
arrangement of the cells, but is always confined to the lower part of the 
fertilized archegonium. 
More than one tier of cells takes part in the formation of the suspensor. 
