we 
: 
THE AMERICAN MIDLAND NATURALIST 83 
of the stele. The larger vessels of the hadrome are mostly reti- 
culately pitted (Fig. 14, 8 and 2) and scalariform pitted (Fig. 
14, 1). The articulations of the reticulate vessels where the 
absorbed transverse walls existed are not uncommonly met with 
(Fig. 14, 8, 2). The vessels of small caliber are usually of the 
spiral, reticulate and occasionally of the annular type. Scleren- 
chymatous tissue (wood-fibres) (tracheids) were always found 
to be present in old roots. The fibres (tracheids) are about 20 
times as long as they are broad, tapering at each end and estab- 
lishing communications with one another by pits. The leptome 
is not well developed in which the tubes with rugged walls are 
from 5—10.5 times longer than they are broad. 
The longitudinal section of the old root (Fig. 14) shows these 
"in order from without inward, dermatogen Ep., hypodermis Hy., 
periblem Cp., endodermis En., pericycle Pe., leptome L., and 
lastly hadrome H., composed of scalariform pitted (1), reticu- 
lately pitted (8-2), spiral (4), and annular (6) vessels, with two 
strands of wood fibres.( 3). 
THE RuHIZOME. (Fig. 15-16). 
The cell structure of the epidermis possesses the same external 
wall thickenings that the dermatogen of the root. Immediately 
under the epidermis are the cells of the hypodermis which are 
nearly twice as long as broad and as shown in longitudinal section 
(Fig. 16) together with the epidermis are being replaced by cork 
tissue (Co) formed from the newly developed phellogen (Ph). 
The periderm is composed of thinner-walled parenchyma cells 
(Phelloderm) toward the inside (not shown in section) and brick- 
shaped cells with suberized walls in very close union toward the 
outside separated by the cork-cambium. The outer cortical 
parenchyma is not as compactly arranged as that nearer the 
stele. The cells vary in shape not uncommonly isodiametric, and 
have much starch. The starch grains are found even in the epi- 
dermis." The endodermis stands out clearly both in cross and 
longitudinal sections, differing in no way from that of the root. 
The fibrovascular bundles are of the collateral type with 
hadrome inferior to the leptome the former appearing as a 
solid hollow cylinder (Siphonostele). The sieve-tubes reach 
but half the elongation that they do in roots, and are less sym- 
metrical as to their lateral wall arrangement. In cross section 
