Substance in Indigo-yielding Plants . 303 
rib and approaches more nearly to that of the stem, in that the vascular 
strand has lost its dorso-ventral character and become completely circular, 
enclosing a central pith. There are two minor vascular strands situated in 
the two dorso-lateral ridges. Both the xylem and the cortex show a 
marked development of fibrous tissue which, in the latter case, forms 
a complete ring enclosing the* central vascular strand. There are also 
numerous cells, situated both in the cortex and pith, which form an 
incomplete laticiferous system. 
Considering the vascular cylinder first, we find indigo deposited in 
some quantity in the pith, except in the apparent laticiferous system where 
no trace occurs ; it is also deposited in the cells forming the medullary 
rays. In the xylem it is completely absent from the vessels ; traces alone 
occur in the fibres ; while there is an abundant deposition in the xylem- 
parenchyma. Indigo is present in all elements of the phloem. In all the 
cortical elements indigo is abundantly deposited, the above-mentioned cells 
of the laticiferous system alone forming an exception. Here no indigo 
is found. In the fibres there is a considerable deposition (Figs. 7, 8). 
Stem. Indigo is only present in the young stem ; as the distance 
from the growing point increases, the amount of indigo becomes progres- 
sively less and finally disappears. Deposition occurs in all the elements 
except, as before, in the xylem-vessels and laticiferous cells. For the first 
time a permanent cambium is found, in the cells of which indigo is 
deposited (Fig. 9). The phloem is bounded externally by a very definite 
and strongly developed fibrous layer, and outside this lies a well-defined 
endodermis. In the cells of both of these indigo occurs. Cortical fibres 
are not present, but the stem is strengthened by a considerable develop- 
ment of sclerenchyma at the angles opposite the primary bundles. In this 
sclerenchymatous tissue indigo is found deposited (Fig. 10). The epidermis, 
as before, contains blue deposited in the normal cells, guard-cells, and 
epidermal hairs. 
Throughout the stem, however, the amount of blue deposited is 
relatively small. It is apparent to the naked eye, after the chlorophyll has 
been extracted with alcohol, as a faint though distinct blue colour which is 
very different to the deep blue of the rachis and leaflet. The abundant 
deposition in these latter ends abruptly at the swollen and somewhat 
prominent pulvinus. 
Roots. There is no indication that the indigo-forming substance occurs 
in these. 
Organs of Reproduction. The flowers of both species are small and 
only rendered conspicuous by the red colour of the two alae. The dis- 
tribution of the indigo-forming substance varies slightly in the two species. 
In the calyx of I. sumatrana a considerable amount of deposition takes 
place, while, in all cases examined, that of I. arrecta showed a complete 
