1916] JEFFREY & TORREY—GINKGO 283 
of magnification transfusion elements above tracheids, which are 
in turn in intimate contact below with the fibrously thickened 
mechanical elements of the sporangium. Fig. 6 shows still another 
view of the tracheids, transfusion and mechanical elements demon- 
strating their continuity with one another at the termination of 
the bundle. Below lies a group of spores. Fig. 7 further illustrates, 
under a considerable degree of magnification, the almost imper- 
ceptible transition from the tracheary and transfusion elements 
of the fibrovascular bundle proper to the reticulated cells which 
constitute the opening mechanism of the sporangium. To the 
right in the median horizontal line lie two narrow tracheids. Above 
and also to the left of these are to be seen transfusion cells with 
reticulated walls of the type characteristic of Ginkgo and certain 
Abietineae. Inferiorly the tracheids abut immediately upon the 
reticulated elements of the mechanical or fibrous layer. 
Fig. 8 represents the vascular system of the microsporophyll in 
transverse section. Sporangia lie to the right and left with con- 
tained spores. The two vascular strands which are present in the 
terminal portion of the sporophyll of Ginkgo end as such at the 
base of the sporangia. Directly above the sporangial cavities on 
either hand are masses of small cells, which constitute the phloem 
of the vascular bundles. The position of the xylem is less apparent 
and is marked by crosses lying inside the islands of phloem. As 
the vicinity of the sporangia is reached the fibrovascular strands 
turn outward, so that the phloem now lies external to the xylem 
instead of below it, as in the lower region of the sporophyll. In the 
median region a large amount of mechanical tissue is present, 
Separating the sporangia and continuous with the ends and sides 
of the xylem of the strands. Fig. 9 represents a more highly mag- 
nified and somewhat oblique view of the situation illustrated in 
fig. 8. To the right may be seen the small elements of the proto- 
xylem of the bundle of the dextral sporangium. On the left the 
sinstral strand of xylem is obliquely cut, showing pits and reticu- 
lations. Farther to the left it passes imperceptibly into the mechan- 
ical elements of the wall of the sporangium. 
€ may now turn with advantage to the diagrammatic fig. 17. 
Here the fibrovascular tissues are shown as penetrating the stalk 
