140 
JOHN T. BUCHHOLZ 
ACTINOSTROBUS AND CaLLISTRIS 
The Actinostrobus and Callitris type of embryo development (figs. 
68-76) has certainly been derived from one of the types already described, 
probably from that of the Cupressineae. In Actinostrobus (35), the first 
walls appear earlier, between the two- and the four-nucleate stages. The 
proembryo tissue fills the entire egg, and the separate embryo initials are 
not organized from the first walled cells, as in Pinus, but after one of the 
Figs. 68-76. Diagrams to represent proembryo of Actinostrobus. Callitris, and 
probably Widderingtonia, are very similar. After Saxton (35). Fig. 77. Gametophytes 
of Callitris, showing large lateral archegonial complex, in its relation to the pollen tube (t). 
After Saxton (34). 
succeeding divisions. Two of the first walled cells undergo no further de- 
velopment, and four embryo initials are organized in the remainder of the 
egg. Figure 77 shows the relation of the gametophytes and the lateral 
archegonial complex in Callitris. From this it will be seen that the embryos 
which grow out laterally from these archegonia penetrate the gametophyte 
in the usual manner. Saxton, to whom we are indebted for our knowledge 
of this interesting embryogeny, states that Callitris (34) is very similar, 
while Widderingtonia (32, 33) is transitional between this and some of the 
Cupressineae. Cleavage polyembryony is a constant feature, and in all 
probability the apical cell is also found in the first stages of the embryo. 
Widderingtonia, Actinostrobus, and Callitris have been placed in a 
separate sub-family, the Callitroideae, by Saxton (37), largely on the basis 
of the game tophy tic and embryonic characters, and it seems that there is 
good ground for including these in a group distinct from the other Cupres- 
sineae. 
