294 



MORPHOLOGY OF GYMNOSPERMS 



at the eight-nucleate stage; but in Thuja and Libocedrus the nuclei 

 pass to the bottom of the egg after the first division, and in Juniperus 

 the fusion nucleus takes this position before dividing. Whether this 

 indicates a general situation among the Cupressineae or not remains 

 to be seen. As among the Taxodineae, the proembryo consists of 

 three tiers of cells, the uppermost one being open above, but its nuclei 



361 



Figs. 361-363. — Juniperus communis: proembryo and early embryo; fig. 361, 

 suspensor beginning to elongate; X430; fig. 362, about the same stage; the large 

 nucleus at the top is "presumably the ventral canal nucleus"; X40S; fig. 363, con- 

 tinued elongation of suspensor; X230. — After Noren. 



soon disintegrate in Thuja. The four cells of the embryo tier in 

 Thuja are not in one plane, having a tetrahedral arrangement. In 

 Widdringtonia and Callitris (159, 176) the details of proembryo- 

 formation have not been observed, but the completed proembryo 

 completely fills the egg with a tissue of eight or more cells, resembling 

 in general the proembryo of Sequoia. Saxton states (176), further- 

 more, that walls appear in the proembryo of Widdringtonia before the 

 eight-nucleate stage, which probably means that they appear during 



