366 BOTANICAL GAZETTE [NOVEMBER 
which ensheaths the younger primordium with its more slender edge, 
ascends in the petioles on the inner or dorsal portion, and branches 
repeatedly. Trace L, has its origin near and to the right of the 
protoxylem group px?, describes a girdle of approximately the same 
magnitude as girdle L4, and runs into the base of the leaf on the right 
hand. Traces L? and L3 have their origin respectively on the right 
and left of the protoxylem group px? (quite close to it), and after 
ascending for a short distance run directly into the outer or ventral 
portion of the leaf, where they ascend without further branching. 
These facts seem to indicate that there is some relationship between 
the protoxylem groups of the vascular plate and the origin of the trace 
of the first leaves. The traces of the third leaf (L,) are followed 
with some difficulty, but the same condition noted for the first and 
second leaves is clear. When a fourth leaf is far enough advanced, 
exactly the same conditions are also presented. The girdling habit 
of the very young strands is already marked out; but their origin 
appears no longer to be restricted to the neighborhood of the protoxy- 
lem groups, but may occur anywhere in the plate, from which they 
how ascend vertically for a longer distance before turning out into the 
cortex. It is very difficult, however, to follow the younger strands 
while they are still in the potential vascular tissue, since no xylem 
elements have as yet been formed; but in their passage through the 
cortex into the primordium their path may be made out clearly, and It 
shows that the girdle is already established at this stage. Even ™ 
the absence of xylem elements, the bundle is clearly marked off by 
the character and arrangement of its cells (jigs. 26, 27). 
Although the specific case described represents the general state 
of affairs, many variations are found in the place of origin of the trace. 
Of the many specimens examined probably no two traces were foun 
i be exactly alike in this respect; also anastomoses between adjoin- 
ing traces were found here and there. The strands thus ascending 
vertically for a short distance into the procambial tissue above the 
vascular plate are the first to assume specific characters. Although 
- ce cylinder is made up of separate traces, it must be observ’ 
at these are in the procambial tissue, which is very different from 
that which surrounds the procambium. 
The transition from endarch to exarch xylem.—When 4 cotyle: 
