Fes. 1909.] | BOTANICAL SOCIETY OF EDINBURGH 21 
the leaf a root can be seen flattened against the trunk. On 
emerging from the leaf-sheath they become cylindrical in 
form and branch freely. Some of these flattened roots can 
be seen in the centre of the figure lower down on the stem. 
Three distinct stages may be noticed in the life-history 
of these aerial roots. The young roots emerge as soft green 
structures, provided with a root-cap. They lengthen, and 
the root-cap is loosened, hanging from the tip of the root 
and easily dislodged by artificial means. This constitutes 
the second stage in the metamorphosis of these roots. The 
final stage is reached when the root-cap is lost, and the root 
becomes completely hardened, forming a thorn. 
These stages can all be distinctly seen in the figure. 
These constitute the changes for unbranched roots, and also 
for the longer branched roots, the lateral roots of which 
ditfer in no respect from the unbranched ones. There are 
many other aerial roots, however, especially at the base of 
the tree forming a dense interwoven thicket, which do not 
harden and become thorns, but, entering the ground, develop 
as normal roots, and perform much the same function as 
the prop-roots in Pandanus. 
The internal features of these aerial roots have been so 
minutely described that there is very little toadd. Buta 
summary may be given of Dr. Friedrich’s results, together 
with one or two interesting points that have been over- 
looked. 
Looking at a longitudinal section of a young aerial root, 
and comparing it with a typical root-cap, say, for instance, 
that of barley, the difference will at once be noticed. In 
the latter case the loose cells are approximately the same 
size, and there is no differentiation into an outer and an 
inner root-cap as in the former (see Plate IT. tig. 2). “The 
cells of the outer root-cap,” to quote Dr. Friedrich, “are 
parenchymatous, and arranged in a brick-shaped manner 
one above the other; their walls are thickened, pitted, and 
markedly lignified (showing an intensive yellow coloration 
with aniline sulphate). Between them are distinct inter- 
cellular spaces. The inner root-cap is distinguished from 
the outer by the different shape of its cells, which are 
smaller, more polyhedric, parenchymatous cells formed by 
tangential division” (Plate II. figs. 2 and 3). 
