20 Tansley and Chick . — Notes on the 
(i) Hydrom, (2) Leptom, (3) Conjunctive tissue, which last we 
may again divide into (a) stereom (central), (b) unlignified 
cells without starch (pericyclic arcs), and (c) unlignified 
cells with starch ( amylom , situated between hydrom and 
leptom). The fundamental resemblance of this (except for 
the curious fact of the absence of starch from the pericyclic 
arcs) to the arrangement of tissues in the stele of a vascular 
plant is sufficiently clear, though the differentiation is dis- 
tinctly less, especially between the different regions of con- 
junctive. The entire absence of pits, so far as we have 
observed, from the tissues of the rhizome is a curious character. 
It is, however, to be noted that the end-walls of all the 
comparatively thick-walled cells, except the hypodermal 
fibres, are much thinner than the side-walls. This is especially 
the case in the regions of conjunctive b and c , and in the inner 
cells of the radial strand. It is to be presumed that the last 
two tissues carry on a large part of the carbohydrate con- 
duction. The pericyclic arcs, we imagine, must be concerned 
in the conduction of nitrogenous compounds, for though its 
cells are not differentiated as leptoids, the only obvious 
difference is the absence of bulging at the junction of 
two cells, and the somewhat greater thickness of their end- 
walls. 
The constancy of starch-distribution in all the sections we 
have examined, not only in the rhizome but in the aerial stem, 
is a striking character. Without this indeed, it would be 
impossible to separate the slightly differentiated tissues to 
the extent we have been able to do. We have examined 
plants in different conditions, both when growth was actively 
proceeding and when it was at a standstill, shoots in a 
purely vegetative state and others during the development 
of the sporogonium, but though there is great variation in the 
amount of starch present, we have found it constantly present 
in some tissues and constantly absent in others. We have 
never seen starch in leptoids although Haberlandt says it 
occurs in them when conduction is slow. We find that 
starch increases very much, cramming the characteristically 
