Seed-vessel of Chara hispida.
a, Part of the stem with the seed-vessel attached. Magnified.
b, Natural size of the seed vessel.
c, Integument of the Gyrogonite, or petrified seed-vessel of Chara hispida, found in the Scotch marl-lakes. Magnified.
d, Section showing the nut within the integument.
e, Lower end of the integument to which the stem was attached.
f, Upper end of the integument to which the stigmata were attached.
g, One of the spiral valves of c.
The seed-vessel of these plants is remarkably tough and hard, and consists of a membranous nut covered by an integument (d, [fig. 102].) both of which are spirally striated or ribbed. The integument is composed of five spiral valves, of a quadrangular form (g). In Chara hispida, which abounds in the lakes of Forfarshire, and which has become fossil in the Bakie Loch, each of the spiral valves of the seed-vessel turns rather more than twice round the circumference, the whole together making between ten and eleven rings. The number of these rings differs greatly in different species, but in the same appears to be very constant.
The stems of Charæ occur fossil in the Scotch marl in great abundance. In some species, as in Chara hispida, the plant when living contains so much carbonate of lime in its vegetable organization, independently of calcareous incrustation, that it effervesces strongly with acids when dry. The stems of Chara hispida are longitudinally striated, with a tendency to be spiral. These striæ, as appears to be the case with all Charæ, turn always like the worm of a screw from right to left, while those of the seed-vessel wind round in a contrary direction. A cross section of the stem exhibits a curious structure, for it is composed of a large tube surrounded by smaller tubes ([fig. 103]., b, c) as is seen in some extinct as well as recent species. In the stems of several species, however, there is only a single tube.[1099]