CONIFERALES (PINACEAE) 295 



the transition from the four-nucleate to the eight-nucleate stage, 

 as in most Pinaceae. 



In these three tribes of Pinaceae, therefore, the proembryo con- 

 sists of twelve to sixteen cells, arranged in three (Taxodineae and 

 Cupressineae) or four (Abietineae) tiers, the fewer cells belonging 

 to the Cupressineae; a statement that must exclude Sequoia, 

 Widdringtonia, and Callitris. 



THE SUSPENSOR AND EMBRYO 



The suspensor cells elongate, thrusting the embryo into the endo- 

 sperm and becoming long and tortuous (figs. 364, 365). In Pinus, 

 where there is a suspensor cell for each embryo cell, four separate 

 embryos develop from each egg (247). Fig. 365a shows ten of the 

 twelve embryos from three eggs. In Taxodium, where there is an 

 inequahty in the number of suspensor and embryo cells, the former 

 may or may not separate from each other, resulting in one or more 

 embryos. In such a case as Thuja, in which the embryo cells are 

 not in one plane, a single embryo is formed. 



In many of the Pinaceae embryonal tubes are developed from the 

 basal cells of the embryo. InPinus (247) these embryonal tubes elon- 

 gate at first singly, later in groups of two or more, forming a second- 

 ary addition to the suspensor between the embryos and their primary 

 suspensors. The upper portion of this suspensor coils back into the 

 funnel-shaped cavity at the archegonial end of the gametophyte, 

 while the other end of the suspensor becomes massive as the embryo 

 increases in diameter. The embryonal tubes are formed by cells from 

 the base of the embryo, no cell divisions occurring in them after they 

 begin to elongate, no matter how long they may become. Figs. 365, 

 365(1, and 366 show them in various stages of elongation. Sections 

 through a secondary suspensor two ceUs wide may look like the lower 

 portion of the early primary suspensorwhen the rosette is not in view. 



BucHHOLZ (247) has also shown that in Pinus the earher 

 divisions are more or less definite, that an apical cell stage exists 

 which cuts off segments transversely, later obhquely with two or 

 more cutting faces, disappearing as the embryo becomes massive, 

 before any of the body regions organize. The organization of the 

 great body regions has not been investigated, so that between 



