1910] SAXTON—EMBRYO OF ENCEPHALARTOS 15 
dotted line is drawn in detail in jig. 5. The group of suspensor- 
forming cells has now become the root meristem, and is not sharply 
differentiated from the distal part of the suspensor. At this stage 
cell division has recommenced in the distal half of the embryo, though 
as yet no further differentiation has taken place. 
The first appearance of the cotyledons is shown in fig. 6. They 
clearly arise, as described for Ginkgo by Lyon,’ by the more rapid 
growth of two groups of cells of the distal meristem. The cotyledons 
of Pinus also are initiated by the more rapid growth of groups of 
cells of the apical meristem,® and it is probable that this is normally 
the case in all gymnosperms. The dermatogen is distinct at this 
Stage, and the root meristem is more clearly shown than in /ig. 5. 
The latter point is shown better in fig. 7, where the central part of 
jig. 6 is drawn in detail. 
Figs. 8, 9, and 10 show later stages, in which the principal changes 
are the elongation of the cotyledons and the development of the 
canals. The first indications of the formation of canals can be 
seen in the stage outlined in jig. 9, and their position is indicated in 
fig. 10. The canal marked «x in fig. ro is drawn in detail in fig. 11. 
The dense contents contain tannin, and probably mucilage also, 
though it is not easy to demonstrate its presence. The canals are 
formed lysigenously, that is, by the breaking-down of rows of cells. 
The boundary of the root meristem is indicated by a dotted line in 
figs.g and ro. In the stage represented by fig. ro the tissue lying 
between the apical meristem and the root meristem is beginning to 
lose its meristematic character; the cells of this region are somewhat 
flattened longitudinally. Figs. z2-15 show the outline of transverse 
sections of an embryo of approximately the same age as that drawn 
in longitudinal section in fig. 10. Fig. 12 shows the base of the 
cotyledons and their attachment to the stem; fig. 13 is taken just 
below the stem apex; fig. 14 is somewhat higher up; and jig. 15 is 
near the apex of the cotyledons. The principal point shown by this 
Series is that at this stage the cotyledons are fused only in the proximal 
half of their length. 
7 Lyon, H. L., The embr f Gink Minn. Bot. Studies 3:275-290. 
, 3 yogeny of Ginkgo. inn. Bot. Stu 3:275-29 
pls. 20-43. 1904. 
s en The writer hopes to publish later an account of the development of the embryo 
inus, 
