1918] BUCHHOLZ—PINUS 203 
cell to the left. For instance, if it is the upper right cell, then 
either the cell below it or the one in the same plane of focus beside 
it is its last segment, while the remaining 2 cells together consti- 
tute the next to the last segment. The other cells of the embryo 
may well have arisen while the apical cell had 1 cutting face. 
Fig. 13 shows a case very similar to fig. 21a, but somewhat 
younger. If the apical cell and the last segment shown here 
should both divide with walls in the plane of the paper, and the 
next tier of 2 cells above this (e;) should do the same, it would not 
differ essentially from fig. 21a, 6. Fig. 14 is in the same stage as 
fig. 13, but with the e, suspensor division elongated. 
- In longitudinal sections the apical cell and its segmentation 
may usually be seen (figs. 25-29). Fig. 31 is an embryo of about 
200 cells, one of the smallest embryos that could be found without 
an apical cell, and fig. 30 is a larger embryo of about 275 cells, which 
apparently still has one. Fig. 32 shows a larger embryo of 750 
cells which no longer has an apical cell; and figs. 35a and 356 show 
the first 2 sections through the end of an embryo in which the 
apical cell is replaced by a meristematic group. Figs. 34a to 34d 
are consecutive cross-sections through an embryo a little larger 
than that of fig. 32, in which the apical cell may still be found, prob- 
ably in an arrested condition, before the meristematic group of cells 
has become active. Fig. 34e is a diagram combining sections 
344 to 34¢ and showing the relation of the segments to the apical 
cell. 
Figs. 33a and 330, sections through the tip of an embryo slightly 
smaller, show an apical cell and segments as diagrammed in fig. 33¢. 
This shows the segments arranged clockwise, while in fig. 34¢ 
they are counter-clockwise. This difference is easily accounted for, 
since the serial sections on these 2 slides run in opposite direc- 
tions through the embryos. In fig. 34 the views of the cross- 
sections proceed toward the apical cell from the base of the embryo, 
while in fig. 33 they proceed from the apex inward. The segments 
thus appear in the same order on the embryo and proceed in the 
same direction as the thread of a wood screw, beginning at the point 
_ which corresponds to the apical cell and passing back along the 
thread toward the older segments. This is probably the usual 
