FERNS. 
75 
themselves from the woody substance, in all directions, and 
consist of tender, annular, and spiral vessels, and a few de- 
licate oblong cells. The stem of Isoetes, like the other vas- 
cular Cryptogamia, has a vegetatio terminalis ; the woody 
bundles do not form any layers with progressing age, but only 
lengthen at their upper end. With regard, however, to the 
parenchymatous part of the stem, the peculiarity is seen 
which we have mentioned before, namely, — 'that the whole 
parenchymatous substance is annually replaced by a new one, 
which developes itself in the circumference of the woody 
bundles, is forced towards the outside, withers, and at last 
decays altogether. The author says, in conclusion, ‘‘ It must 
be regarded as very improbable, when the mode of germina- 
tion of the other Cryptogamia, from which the germination of 
Isoetes certainly does not materially deviate, is considered, 
that these plants possess a real Caudex descendens. Since, 
however, the development of the root fibres takes place in a 
descending order, and since the central woody substance, 
from which the vessels of the fibres are derived, extend them- 
selves downwards ; we have, perhaps, in Isoetes, an instance 
before us of the case, which is so distinctly exhibited by Tamus 
communis, namely, — that the lower part of the rising axis 
developes itself, in relation to its growth, in the same manner 
as an original Caudex descendens, without being so in reality.” 
It would have been desirable that the author should have 
examined Isoetes setacea, which is easier to be obtained than 
Isoetes lacustris ; it grows after the root-stock has been dried 
for some time. 
The remarkable phenomenon which M. Martens first ob- 
served at Lowen, in the botanical garden, that an inter- 
mediate species of fern grew where Gymnogramma calome- 
lanos and chrysophylla were situated, has also been observed 
by Bernhardi in Erfurt (Ottos and Dietrichs Flora, 1840, 
p. 249 and 325). A fern has grown in the botanical garden 
of that place, which holds a middle rank between Gymno- 
gramma distans and chrysophylla, species which are culti- 
vated in the same garden, and had been frequently standing 
next to each other. The frond of this intermediate fern is 
467 
