CONIFERALES (TAXACEAE) 



347 



until eight or sixteen free nuclei are produced, when wall-formation 

 occurs, the completed proembryo consisting of sixteen or thirty-two 

 cells. These cells form fairly definite tiers above, but become more 

 or less irregularly arranged below. Four regions or tiers may be 

 recognized, at least so far as their functions are concerned: open 

 tier (open above), suspensor tier, embryo-forming region, and region 

 of the "penetrating cap," which last is a peculiar feature of the genus 

 (figs. 369, 370). In Taxus there are also sixteen free nuclei before 

 wall-formation. 



Figs. 401, 402. — Torreya taxifolia: fig. 401, four-nucleate stage of proembryo; 

 August 12, 1904; X460; fig. 402, proembryo showing the three tiers of cells; the 

 entire egg is segmented; the proembryo passes the winter in this stage; August 27, 

 1904; X460. — After Coulter and Land (ioi). 



Among the podocarps Podocarpus (69) and Phyllocladus (144) 

 have been investigated. In the former genus the fusion nucleus 

 assumes the basal position, and sixteen free nuclei appear before 

 wall-formation. The three tiers of the completed proembryo are 

 made up as follows: fourteen cells in the open tier, fourteen in the 

 suspensor tier, and one binucleate cell in the embryo-forming tier. 

 In Phyllocladus there are eight free nuclei before wall-formation. 



Among the Pinaceae, with the possible exception of the araucarians, 

 wall-formation in connection with the mitosis which gives rise to 

 the eight-nucleate stage of the proembryo is a remarkably uniform 



