12 INTRODUCTION. INTRODUCTION. 13
So extraordinary were the statements from time to time
put forth relatiA’C to the spontaneous motion of the reproductive
germs of many A lga — a class of productions ahvays regarded
as vegetable ■— considered to be, that many observers,
and some do even now, refuse to give their behef to their
accuracy. So numerous are the observers who have witnessed
the singular motions above recorded, that the facts announced
in reference to them must be regarded as amongst those
which ought to be generally received and adopted. F o r a
long time I myself doubted the reality of the existence of
zoospores; I have now satisfied myself on this head, having
repeatedly witnessed their movements in very many Conferva,
but never as yet in any species belonging to the conjugativc
tribe of A lg a ; in whicli, however, Agardh declares himself
to have witnessed it. For extended observations on the
motion of the zoospores of the Alga, see, in “ Annales des
Sciences Naturelles (Botanlque), 1836,” a memoir “ Sur la
Propagation des Algues. P a r J . G. Agardh. E x trait.”
I t is surprising that, out of the number of those
wdio now study the Alga, so few should have witnessed
the singular motion of the zoospores. The spring is the
best season for observing these bodies. If, at tha t time,
a number of Alga, collected indiscriminately from different
locahties, are placed in a vessel of water over-night, and
allowed to remain undisturbed until the morning, usually
there will be noticed on the surface of the water a thin
green pellicle or scum: this, when examined, will be found
to consist of the zoospores of different species of Conferva,
in all possible stages of developement. Their motion is
most active early in the morning; and they would appear
to shun the light, as they are generally met Avith on the
side of the vessel farthest removed therefrom.
N ex t in interest to the discovery of the zoospores themselves,
and for which science was mainly indebted to the
researches o f J . G. Agardh, is that of the means by Avhich
their motion is effected. J . G. Agardh declared that it
depended upon the movement of a prolongation or beak,
Avith Avhich each zoospore Avas said to be furnished; others
have endeavoured to account for it by reference to the
principle of endosmosis; but neither of these explanations
can be deemed satisfactory; the true cause of it depending,
according to the researches of M. Unger*, and M. Gustave
T h u re tt, upon the presence of cilia, similar to those of the
infusory animalcules. The folloAving abstract of M. Thuret s
paper, on a subject of such high interest, cannot fall of
being acceptable.
The spontaneous movement of the spores of the Algaj
has been vicAved by a great many observers. In certain
cases it is apparent to the unaided s ig h t; but until noAV, as
declares ISI. Dujardln, in his “ Observateur, ou Microscope ”
(Paris, 1843), they have not been able to discover by AA’hat
• means the spores swim in the liquid. Nevertheless, the cilia,
or filiform tentacles, which serve them as locomotive organs,
do not appear to me more difficult to see than the filaments
discovered by M. Dujardin in a great number of Infusoria;
and if they have escaped an observer so practised, it is,
Avithout doubt, because he has not continued his researches
Avith enough of perseverance, or else, tha t he has not made
them in all the conditions necessary for success.
In fine, the movement of the spores continues for some
hours, during which the locomotive organs are in incessant
agitation, and in consequ'ence very difficult to distinguish.
The use of coloured infusions cannot but detect their existence.
When the spore stops, the locomotive organs disappear
very quickly, without leaving any traces, and some
time after, the germination commences. I t is necessary
then to seize the precise instant Avhen the spores cease to
move; or, to make the chances of success greater, it is
necessary, Avhen one finds those which moA'e with vivacity,
to put them in contact with a reagent the action of Avhich is
too feeble to alter their form, but enough to stop their
movements. Opium and iodine appear to me the agents
the most proper to obtain this result.
* Die Pflanze in Momente der Thierwerdung. Wien. 1843.
t Eesearches sur les Organes Locomoteurs des Spores des Algues.
Par M. Gastave Thuret. Ann. des Sciences Nat., Mai et Juin, 1843.