412 Boewig on the Histology and 
ciated with a slight amount of phloem. Internal to these 
and widely separated from them by undifferentiated tissue 
are two solitary wood cells, irregularly placed. All these 
wood elements are decidedly thickened, although the primary 
membrane is well marked. 
The protoxylem early splits up into three and much later 
into a greater number—six to eight—of patches. The pro- 
tophloem patches remain five in number so long as there are 
three patches of protoxylem. 
As soon as the phloem begins to develop hard bast, the 
true phloem disintegrates, and its place is taken by internal 
phloem. Thus are formed five canals external to the wood. 
These canals are more evident and considerably larger in the 
side shoots and tendrils than in the main axis or larger stems. 
In the larger stems there is also more hard bast than in the 
side shoots and tendrils. This seems to show that the 
reduction in amount of true phloem is not a mechanical 
result of the formation of bast, but is rather in line with 
the usual reduction of external phloem in twining stems. 
The internal phloem develops all around the protoxylem. 
The wood spreads until its original patches are quite con- 
fluent around the stem, leaving no trace finally of recog- 
nizable medullary rays. By this time the external phloem, 
now consisting of little more than hard bast, whose cell 
lumen is also by this time almost completely obliterated, 
together with a trace of flattened phloem cells, has broken 
into perhaps twenty patches of varying size, large and small 
ones frequently alternating. The smaller of these have no 
canal and no soft bast. The internal phloem also consists 
of six to ten pointed triangular patches, each with two or 
three protoxylem cells enclosed. 
The development of the bordered pits is clearly traceable 
through all stages and makes a very interesting study. 
In young side shoots, and to a less extent in tendrils, the 
cortex remains more abundant and somewhat more columnar 
than in older ones. 
