166 MORPHOLOGY OF SPERMATOPHYTES 



the nutritive supplies stored up in the egg, (2) a suspensor, which 

 develops from the proembryo and relates the embryo to the 

 nutritive supplies of the endosperm, and (3) the embryo proper. 



In the case of the Coniferales the same sequence is repeated, 

 except that free nuclear division becomes much reduced, usually 

 resulting in but four nuclei, which pass to the base of the oospore 

 and organize a definite basal proembryo of three tiers of cells, 

 with four cells in each tier. It is interesting to note that in 

 Cephalotaxus Fortunei the free nuclear division is not so re- 

 stricted, but results in eight or sixteen free nuclei, which pass 

 to the base and organize the proembryo. The difference be- 

 tween Coniferales and Cycadales, therefore, is that in the for- 

 mer the number of free nuclei is restricted, and therefore the 

 formation of a proembryonic tissue takes place only in the basal 

 region of the oospore. In both cases the suspensor is formed by 

 the elongation of some of the cells of the proembryo, and in 

 Coniferales a single plate ("rosette") of cells retains connec- 

 tion with the nutritive supplies of the oospore, rather than a 

 parietal layer. Another feature in the formation of the pro- 

 embryo of Coniferales is worthy of note. The first walls formed 

 about the nuclei of the primary basal group are not an accom- 

 paniment of nuclear division, but seem to be formed directly by 

 fibers investing the nuclei, and they do not cut off these nuclei 

 from the general cavity of the oospore above. The subsequent 

 walls which result in building up the tiers are associated with 

 nuclear division, but the uppermost nuclei always remain ex- 

 posed to the cavity of the oospore, and are separated from one 

 another by walls which extend more or less into the mass of the 

 oospore. 



In Ephedra free nuclear division also occurs, two to eight 

 such nuclei being formed, but they organize as free cells, and 

 do not form a definite tissue. As a consequence, the cells act 

 independently, and each one develops a long tubular process 

 (suspensor), the bulbous base remaining in touch with the nutri- 

 tive supplies of the spore, and at the tip of each suspensor an 

 embryonic cell is cut off. This independence of the cells may 

 be observed also in Pinus, where, although there is a regular 

 tier formation of the proembryo, each cell of the suspensor 

 set develops a separate suspensor bearing at its tip an em- 

 bryonic cell. 



