Hill. — On the Roots of Bignonia . 325 
We will now turn to a more detailed description of the 
root-structure in various species. 
Bignonia Unguis. In this species the anomalous structure 
of the stem is undoubtedly present in the root. The structure 
of the normal root without any sunken phloem is illustrated 
by Fig. 1, the protoxylem and the medullary rays are well 
marked and quite typical. With this illustration might be 
compared Fig. 2, which is a somewhat diagrammatic repre- 
sentation of a transverse section of an older part of the root 
figured in Fig. 1. It will be observed that the formation 
of sunken phloem has gone on to some extent. 
The first indication of the sunken phloem makes its 
appearance in quite small roots from -8 to 1 mm. in diameter, 
with five to ten cells in the radial rows of secondary wood. 
Such a stage is indicated in Fig. 3, which illustrates a trans- 
verse section of a young root. It will be seen that that 
protoxylem ( pxy ) is well marked, and is typically that of 
a root both as regards structure and position ; secondary 
growth of wood has not gone on to any great extent ; the 
phloem exhibits very fine sieve-tubes and companion-cells; 
and finally the cortical sclerenchyma is made up of fibres 
lignified to a very great extent, so that the lumina are quite 
small. In these fibres very fine simple pits were to be seen in 
the preparation from which this figure was taken. 
On the other hand, in some roots with about 2 6 cells 
in the radial rows of secondary wood the process has not 
gone much farther; thus it seems that the development of 
the sunken phloem does not originate at the same time in 
equally developed roots. In roots of about 1*3 mm. diameter 
the development has proceeded until, with a diameter of 
1-76 mm., the stage has reached that figured in Fig. 4. In 
some roots of a smaller diameter than the last, viz. 1-5 mm., 
the development has gone on to a greater extent, the sunken 
phloem being -28 to *3 mm. in depth (measured from the 
outer limit of the wood). Such a stage is indicated in Fig. 5. 
Criiger 1 states that the anomaly is not so regular as in 
1 Loc. cit. 
Z 
