4 i6 Scott and Hill.—Structure of Isoetes Hystrix. 
duction. The conditions under which fertilization and dis¬ 
semination take place appear to deserve investigation. Pos¬ 
sibly earthworms may play some part in the matter. 
The Stem. 
The general structure of the stem of Isoetes has been known 
for many years. A very accurate account of its main features, 
as shown in /. lacustris , a two-furrowed species, was given 
by v. Mohl in 1840, and his bold, diagrammatic figures are 
admirably adapted to give an idea of its peculiarities. From 
that time onwards our present knowledge of the stem- 
structure has been gradually built up by the successive 
labours of Hofmeister, Alexander Braun, Russow, Hegelmaier, 
Bruchmann, Farmer, and others. Our knowledge is still 
imperfect as regards the mode of growth at the apex, the 
differentiation of the tissues, and the nature of the secondary 
growth. On these points we hope that some new light is 
thrown by our observations, to which we will now pass on, 
dealing with the statements in the literature as we proceed. 
The short, three-lobed stem of Isoetes Hystrix has a deep 
depression at the apex, at the bottom of which the growing- 
point is situated. The sloping sides of the funnel-shaped 
depression are covered by the leaves, becoming successively 
younger as they approach the growing-point at the bottom 
of the funnel. In these respects there is no essential difference 
from the stem of other species, and various figures in the 
literature will serve to illustrate the general arrangement 1 . 
The growth of the stem in length is extremely slow, while 
the cortex, owing to the extension of the primary tissues, 
and to cambial activity, has a vigorous circumferential increase. 
It is the extraordinarily stunted form of the Isoetes -stem 
which gives rise to most of its peculiarities. 
The stem is traversed longitudinally by a single stele; in 
its upper part the stele is cylindrical, while lower down the 
1 See, for example, v. Mohl, 1845, PI. V, Figs. 9 and 10; Hofmeister, 1852, 
PI. X, Fig. 1, PI. XII, Fig. 1, &c.; Wilson Smith, 1900, PI. XIII, Figs. 3 and 4. 
