592 F, 0. BOWER. 
4. The directions of cell division at the base of the leaf groove 
are such as to bring about— . 
(a) Increase in length of the leaf. 
(4) Increase in length of the whole plant. 
(c) Increase of the tissues in a direction perpendicular to the 
surface of the groove, and hence increase in bulk of the crown 
on the one hand, and of the stock on the other. 
5. The two originally separate primary xylem masses of the 
root unite centrally at a short distance below the feeder, so as to 
form a single plate. Above the point of union a parenchymatous 
pith remains permanently between them. 
6. Further development proceeds in a direction at right 
angles to this plate, by means of a cambium layer. The result 
is the formation of two masses of secondary vascular tissue sepa- 
rated laterally from one another by two broad medullary rays. 
Thus far the structure corresponds to that described for Ephedra 
(cf. Van Tieghem, La Racine, p. 211). 
7. Smaller vascular bundles separate laterally from these 
masses of secondary vascular tissue, and pursue a sinuous course 
along the medullary rays, fusing from time to time (a) laterally 
with the system from which they were derived, and (4) with the 
later developed system of peripheral bundles. These bundles 
may be compared with the intercalary bundles of many dicoty- 
ledonous stems (Zwischenstringe, De Bary, ‘ Vergl. Anat.,’ 
p- 468). 
8. Peripheral bundles appear later; their terminations I 
have not been able to trace. They are formed by the specially 
localised activity of division in the parenchymatous “ ground 
tissue,” and are arranged in more or less regular rings. 
9. All bundles of the root remain for a considerable time 
open bundles, and by the activity of their cambium may attain a 
large size. This is especially the case in the central group. 
10. In the arrangement of the vascular bundles of the older 
plant at the point of transition from root to stem, there may be 
traced a very close relationship to the arrangement at the same 
point in the seedling. The differences are due to (1) increase in 
size and number of vascular bundles, the later formed bundles 
being, however, mainly grouped around the original bundles; 
(2) to increase in bulk of the “ ground tissue,” and consequent 
increase in absolute distance of the original bundles one from 
another. 
11. As they pass up the stock the bundles retain for a time 
an arrangement obviously related to that in the seedling, but as 
the apex is approached this is gradually lost sight of by the 
breaking up of the groups of secondary bundles which lower 
down surround the primary bundles, 
