814 KINGSLEY: SPLITTING OF RHIZOME OF DELPHINIUM 
one of these columns (PLATE 14) directly inside of the cork layer, has 
a circular region of irregular, loose parenchyma (not disintegrated 
to the extent of becoming brown, however). In this loose tissue 
the secondary xylem elements can be seen separated out from the 
third and fourth year elements, all three of which are surrounded 
by a complete ring of endodermis. This endodermis marks the 
outer limit of the regular close cortex, and may become, as secon- 
dary wood and parenchyma are produced inside, so stretched out 
and pushed into outer cortex, that it becomes the seat of activity 
for the production of a new cork region as the disintegrating cortical 
cells invade this central portion farther. 
This column (as shown in PLATE 14) is not perfectly rounded. 
But the presence of a very active meristematic zone inside of the 
former inner endodermis cutting off cells on the inner side, seems 
to account for the final rounding off of these separate members. 
Owing to the necrosis of tissues in the center of older parts, it 
is impossible to determine with any degree of accuracy where rhi- 
zome ends and root begins. To follow out the root changes we 
must begin, as in the case of the stem, with the youngest parts. 
The lower end of one of the final divisions, in cross section, shows a 
diarch root arrangement (FIG. 8), with the axial strand small but 
developed apparently in centripetal order, since the larger ducts 
are in the center, the smaller toward the outside; also since longi- 
tudinal sections show the same order of duct formation—spiral 
toward the outside, pitted toward the center. 
Secondary thickening follows by the activity of a complete 
cambial ring, which cuts off collateral xylem elements and phloem 
opposite the primary bundle strands, and radial rows of paren- 
chyma cells in all the remaining space. In the third layer from 
the outside of the regular parenchyma cells, appears the single 
endodermal row of cells, as in the shoot, cutting off the spongy 
parenchyma from the inner regions. When three years’ xylem 
shows in a section cut farther back (FIG. 9), the central strand is 
surrounded by an endodermis and parenchymalike active cells. 
The loose cortical parenchyma invades the center through the 
groove made by the entering of the outer endodermis, and the 
root is divided. The periderm surrounds the root, and in turn 
each division is completely protected by an active cork layer. 
