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JOHN T. BUCHHOLZ 
this, and hence the tier of cells r (fig. 3), the rosette tier, is also organized 
directly after a free nuclear division in the proembryo. These rosette cells 
are now known to be embryo initials (2). 
In this stage, shown in figure 3, with the upper aborting tier of four 
free nuclei and with eight-walled cells beneath them arranged in two tiers, 
we have the initial cells of all the embryos that are regularly produced 
Figs. 1-8. Embryogeny of Pinus. Figs. 1-4. Sectional views of proembryonic 
stages. Fig. 5. Embryos when suspensors begin elongating. Fig. 6. Separation of 
four embryos coming from p. Embryos arising from rosette {r) are shown in figure 8. 
a, apical cell; s, suspensor; ei, e^, embryonal tubes that add to suspensor; p, tier of initial 
cells of primary embryos; r, rosette tier. 
from a single fertilized egg in the pine. Of course, some of these initials, 
especially those of the rosette group, may abort in this stage or in any subse- 
quent stage of development. 
The embryos that arise from each of these initial cells begin their de- 
velopment by true apical cell growth ; first the apical cell has only one cut- 
ting face, and later, when the embryos have separated, it has three cutting 
faces. The apical cell vanishes, usually before an embryo of more than 500 
cells is formed. 
Following the organization of these eight walled cells, the embryo initials 
of the tier p undergo simultaneous division in which the tier 5 is formed 
(fig. 4). These first segments {s) of their respective apical cells elongate to 
form suspensor cells (figs. 5, 6), while the apical cells {a) form additional 
segments, ^i, e^, etc., that elongate and add to the suspensor. 
By this time the four vertical rows of cells, representing as many em- 
bryos, have separated, and the rosette cells (r) begin to proliferate to form 
the rosette embryos. The four rosette embryos usually do not actually 
