INTRODUCTION. 
15 
axis of double refraction. In the straw and chaff of wheat, barley, oats, and ryet 
he noticed analogous phenomena, but the particles were arranged in a differen 
manner, and ‘ displayed figures of singular beauty.’ From these data, the learned 
doctor concludes, ‘ that the crystalline portions of the 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.’ ” — Breivster MS. 
Thecse and Spob.es. The spores are produced in a terminal spike or catkin 
(a), composed of hexagonal shields (c), from the under side of which depend 
hollow, scale-like thecae (c, d), 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 con- 
siderable distance (e, f, g). 
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 
confirm the above view, and give also the origin of the minute grains found upon 
the elaters or elastic filaments ; from this paper, it appears that when the integu- 
ment of the spore shows the spiral lines, which it will afterwards break into the 
elaters, it contains a greenish-coloured fluid, mixed with some minute granules. 
The spores then become darker, the granules increase, the liquid is absorbed, 
leaving the granules which it contained sticking in masses to the spores, and to 
the separated portions of the integument. These masses of granules, were found 
adhering to the filaments in the ripened state of the spore, taken by him for 
pollen-grains, but this has proved to be erroneous. 
[Germination of the Spores. From the observations that recently have been 
made, it appears that the spores of the Equiseta do not long preserve their 
germinative power, but must be sown when fresh from the thecae. They seem to 
require much moisture and go through their early stages well if scattered on the 
surface of water. The spores germinate much in the same way as those of the 
Ferns, protruding a tubular pouch, which elongates, or expands at its end into a 
minute leaf-like prothallium. Upon these protliallia autheridia and arcliegonia are 
produced; but in E. arvense, pratense, and palustre, and perhaps in the other 
species, the protliallia are dioecious, each producing either only autheridia or 
only arcliegonia. No difference can be detected in the spores which produce the 
different sexes. The male protliallia are smaller than the female, usually of a 
yellower tint, and bear numerous antheridia, which are situated at the margins. 
The female protliallia are ordinarily much rarer than the male, but this, perhaps, 
depends upon external conditions ; they bear the arcliegonia upon distinct 
lobes, and there are often more of them than of antheridia on the male plants 
(20—30); and they come to full development later than the male ones sown at the 
