174 BOTANICAL GAZETTE [MARCH 
condition occurred, as shown in fig. 4; the pith is not xylem paren- 
chyma, but is composed of cells resembling those of the cortex; the 
opening through the xylem always occurs, but the endodermis is 
not interrupted. This occurs only in roots upon which buds have 
developed stems; the open portion of the xylem mass is upon the 
upper side of the root. This condition persists for only a short 
distance from the bud toward the tip of the root; the gap soon 
closes and a solid xylem mass is again formed. This peculiar 
root stele form is directly related to the formation of the stem stele 
from buds upon the roots, as described later. 
The branching of the root is strictly monopodial. The lateral 
roots grow at an angle of 60-90° to the main root; two or three 
branch roots often develop at one point. These are not restricted 
in their growth, as in Helminthostachys, 
but may reach as great length as the 
primary roots. 
Immediately before a branch is given 
off, the phloem of the main stele spreads 
laterally between the endodermis an 
the protoxylem, and forms a continuous 
Fic. 4——Medullated root sheath about the xylem. A strand of 
spa a xylem from each of two poles of the 
main root runs into the branch; hence 
the lateral roots at the point of attachment are diarch. The 
phloem sheath surrounds the xylem of the branch in the same way 
that it does that of the main root; the endodermis also connects 
without a gap. After the branch has separated, the phloem 
between the protoxylem and the endodermis disappears, and the 
usual arrangement of the stelar elements is restored. 
In all cases, the branch stele is diarch at the point of attach- 
ment, but it may arise from a single pole of the main root. The 
protoxylem strands of the branch soon split, and the usual triarch 
or tetrarch condition is established. In one case, a branch arises 
from a large tetrarch root in which lignification has just begun; 
each pole is represented by three or four tracheids only. Two dis- 
tinct strands of xylem, connecting with two poles of the main root, 
enter the branch. Each xylem strand is surrounded by a sheath 
