System of the Female ‘ Flowers' of Conifer ae. 529 
lower side k In the above cases, where the two branches 
from the upper bundle are intercalated between the bundles of 
the lower group, the upper bundle subsequently gives off 
a branch, first on one side, then on the other, each of which 
fuses with the respective lateral bundles of the lower group. 
The lower bract-bundle, both before it cuts off the small upper 
inverted bundle, and at any time during its subsequent 
division, may exhibit centripetal xylem in small quantity ; 
but this tissue is, perhaps, most frequently absent Centri- 
petal xylem occurs both in dorsal and ventral bundles in the 
stalk of the scale, as also in the region of insertion of the 
sporangium ; the tracheides of this tissue are sometimes quite 
short, but often considerably elongated, and with abrupt 
horizontal or slightly oblique terminal walls ; they have very 
dense, fine spiral thickenings just like those of the cen- 
trifugal xylem. 
The sporangium has become imbedded in the tissues of 
what I regard as the seminiferous scale, and has thereby lost 
a portion of its individuality. This has probably taken place 
when the formerly orthotropous sporangium seated on the 
dorsal side of the scale became completely inverted, owing to 
intercalary growth arising below it ; this change occurring 
in order to facilitate fertilization. When this happened, 
a portion of the tissues of the scale probably enwrapped it at 
the same time, enclosing everything except the extreme tip 
of the integument in the micropylar region. The tissues of 
the integument thus became completely fused with those of 
the seminiferous scale, so that no sharp line of demarcation 
any longer existed between them 2 . But the limit of the 
integument can easily be made out ; the latter consists of two 
thick layers : an inner whitish, and an outer yellow tissue, 
formed of irregular, elongated, pointed cells, intermingled like 
the filaments of a fungus and containing elongated nuclei. 
This yellow layer is separated from the tissues of the 
1 A subsequent connexion may occur between one of the two median upper 
bundles and one of the intermediate bundles of the lower groups. 
2 According to my own view as to the nature of the seminiferous scale (see infra), 
this fusion is simply that between an inner and an outer integument. 
