INTRODUCTION. 
17 
order, and which it will he recollected there, as here, are arranged in longitudinal 
lines. A transverse section of the stem shows that between the outer and inner 
cuticle is a circle (and in Equisetum fluviatile two circles, alternating with 
each other), of tubes distinct from each other, but terminating at every joint 
of the stem ; fresh tubes of a similar character being found at every other joint. 
Around these tubes, and especially towards the outside of the whole stem, and 
seated immediately under the cuticle, are the sap-vessels of the plant, which 
appear flat, spiral, perforated ducts, as in the other orders. The inner surface 
of the stem is frequently more silicious than the outer, forming a very beautifu* 
object even to the naked eye. So abundant is this deposit in Equisetum 
hyemale, that, after the vegetable matter has been removed by maceration, the 
silex has been sufficiently abundant to retain the form of the plant. M. John, 
of Berlin, states that the stems contain full 13 per cent, of silica. The following 
interesting particulars of the silicious cuticle of Equisetum is given in Dr. 
Greville’s excellent ‘Flora Edinensis,’ p. 214: “On subjecting a portion of 
the cuticle to the analysis of polarized light, under a high magnifying power, 
Dr. Brewster detected a beautiful arrangement of the silicious particles, which 
are distributed in two lines parallel to the axis of the stem, and extending over 
the whole surface. The greater number of the particles form simple straight 
lines, but the rest are grouped into oval forms, connected together like the 
jewels of a necklace, by a chain of particles forming a sort of curvilinear 
quadrangle; these rows of oval combinations being arranged in pairs. Many 
of those particles which form the straight lines do not exceed the 500th part 
of an inch in diameter. Dr. Brewster also observed the remarkable fact, that 
each particle has a regular axis of double refraction. In the straw and chaff 
of wheat, barley, oats, and rye he noticed analogous phenomena, but the 
particles were arranged in a different manner, and ‘ displayed figures of singular 
beauty.’ From these data, the learned doctor concludes, ‘ that the crystalline 
portions of silex, and other earths which are found in vegetable films, are not 
foreign substances of accidental occurrence, but are integral parts of the plant 
itself, and probably perform some important function in the processes of vegetable 
life.’ ” — Brewster MS. 
REPRODUCTION. — The reproductive organs are borne in a terminal spike 
or catkin, composed of hexagonal or octagonal shields, from each side of which 
depend hollow, scale-like follicles, opening inwardly, and emitting green, ovate 
spores, to each of which is attached four club-shaped filaments. When the 
spores are immature, the filaments are twisted tightly round them ; but when 
ripe, they become exceedingly elastic and hygrometrical, so much so, that the 
irritability occasioned by a change of temperature or moisture, causes the spores 
first to burst the thecae which bear them, and afterwards to scatter themselves to 
a considerable distance. 
A valuable paper upon the formation of the spores, by Mr. Henderson, was 
read before the Linnean Society, in June 1840, and will be found in their 
‘ Transactions,’ vol. xviii, p. 567. The experiments of this gentleman exactly 
