568 Mr. Henverson on the Reproductive Organs of Equisetum. 
from time to time on Equisetum hyemale and other species) I shall endeavour 
to show that the filaments attached to the spores of Equisetum are separated 
portions of an oval integument which envelopes the spore in its early state, 
and which, being attached to it on one side, and opening by spiral sutures or 
slits as the spore approaches to maturity, finally on its escape from the theca 
unrolls, and separates into two filaments with clavate tips attached by their 
middle to the spore. When the spike or fructification of Equisetum hyemale 
first begins to swell beyond the terminal sheath, the spores may be observed 
in a rudimentary state on carefully dissecting the theca, the interior of which 
is at this time divided into cells of extreme tenuity, in wbich the spores 
originate. These cells are filled with a viscid, greenish-coloured fluid, which, 
when mixed with a small portion of water and highly magnified, will be found 
to contain innumerable minute granules, possessing spontaneous motion, and 
moving apparently on their axes with considerable rapidity : they are of various 
sizes (fig. 5.) and of various shapes, the larger generally oblong, the lesser sphe- 
rical: they are all equally active, and being transparent, they communicate a 
whitish colour to the water when viewed with the naked eye. 
Tas. XXXIX. fig. 3. represents four cells detached by means of water, con- 
taining the spores in the position which they occupy within the cells; at first 
their form is oval or ovate, but they very soon change to globular, the form 
which they afterwards retain. It is extremely difficult at this time to detach 
any of these cells entire, owing to the filmy condition of their walls and the 
viscid nature of their contained fluid: a better opportunity is afforded of view- 
ing their form and arrangement by macerating the theca in dilute nitric acid, 
when they appear somewhat shrunk and collapsed, and the minute granules 
are therefore easily discernible in the cells (Tan. XXXIX. fig. 4.) and also in 
the spores: the whole mass is easily forced asunder even to the theca, which 
separates into parts corresponding with the sides of the outer cells. Consider- 
able changés take place in the spores from the state here noticed in their 
progress to maturity; these are accompanied by other and very remarkable 
changes in the theca as well as in the cells. These latter gradually acquire 
substance, separate from each other, and, changing their form, become first 
globular, and afterwards oval integuments of the spores; the spaces caused by 
their separation being filled up with a dark green viscid fluid containing 
