66 Transition from Stem to Root in Palm Seedlings. 
the role of an air-tight sheath allotted to the endodermis by many 
physiologists seems to be well supported from the anatomical side. 
It is with the xylem portion of the bundle that this function of 
the endodermis is generally assumed to be associated. This 
however, is not very clear. In roots the endodermis may be 
provided with non-cuticularized “passage cells.” These cells occur 
opposite the xylem groups, while the cuticularized elements are 
usually continuous over the phloem regions. The frequent reduction 
of xylem in aquatic plants is not necessarily, or even generally, 
associated with reduction in the endodermis. 
In Phoenix and Livistona the endodermis-like sheaths to the 
cotyledonary bundles are frequently incomplete, being wanting on 
the xylem face, though present on the phloem face. Again, in 
ectophloic medullated monosteles the presence of an internal 
endodermis between xylem and central parenchyma is rare; on the 
other hand when an amphiphloic condition obtains, an endodermis 
often cuts off the internal phloem from the central parenchyma. 
It is conceivable that the endodermis may find its function rather 
as a phloem sheath than as a xylem sheath. This is at all events 
possible. Further investigation alone can support or disprove the 
validity of this suggestion. 
There appears to be true transition between the bundles of the 
root and, on the one hand, those of the cotyledon, on the other 
those of the stem. In Monocotyledons it is generally found that 
the continuity is primarily between the root- and cotyledon-bundles 
only, and that the plumular traces are secondarily inserted upon 
these common strands at, or below, the cotyledonary node. In the 
palm seedlings examined, it is true the plumular traces are later in 
differentiation and lignificatlon than the cotyledonary bundles. 
This is to be expected, seeing that the cotyledonary bundles serve as 
conductors of the elaborated food-material from the seeds to the 
growing seedling. At the same time, however, some of the xylem 
and phloem strands of the root are directly and primarily continuous 
with those of the plumule, and have no connection, or only a lateral 
one, with the strands common to root and cotyledon. 
