19
OBSERVATIONS
ON
DESMIDIAOE^,
WITH A
LIST
OF
SPECIES
FOUND
IN
TASMANIA.
[By E. D. Haerop.]
These
beautifulplants are of an herbaceous green color,and
belongtothe Cryptogamicdivisionof the vegetableking-dom.
They
haveattractedattentionnot only on account of thestrikingbeautyand
variety of their forms, but alsoby
reason ofthedoubtas to their position,whetherintheanimalor vegetable kingdom, having caused considerable discussion
amongst
learnedalgologists.They
arenow
almost univers-ally assigned to the vegetable kingdom.The
presence of starch in the ludochrome,and
theirmode
of conjugating,constituteincontestableproofsoftheir vegetableorganisation,
notwithstanding the argumentsof ProfessorsEhrenberg, Dal-rymple,
and
Baileytothecontrary.The
principal arguments in favor of their animality are passed inreview by Ealfs.They
are,—
first, the power of voluntarymotionthatthey possess; second, their increaseby
voluntary division ; third, the definite organ, possessed
by
some
genera, inwhich active molecules appear to enjoyan
independentmotion,and
theparietiesofwhich appearcapable of contractingupon
itscontents; fourth, theswarming
motionwhich takesplace at a certain stage of their growth. Other arguments have been advancedin support of this side ofthe
question,
and
Ehrenbergwent
so far as to describe orifices,havingprotruding organsor feet immediately behind them,
thebasisof such organs being the
moving
molecules whichare always openedat theends of the Closterium.
Notwith-standing the greatimprovement in the microscope since the
time of this distinguished Professor, his observations have
neverbeencorroborated,andthereis little doubt but that in
this instanceheallowedhisimaginationtooverrulehisgeneral accuracy.
The
powerofmotionand
increaseby
self-divisionhavenow
been abandoned asproofs of animality. It is manifest that they can transport themselves or, perhaps are transported
underthesubtleinfluence oflight, from oneplace toanother;
forif a
mass
ofDesmidieae be placedin a glass vase,theoneside of whichisexposedto thesun's rays,
we
shallfind,aftera shorttime, thatmostof
them
have found theirway
to the illuminated sideof the glass. ProfessorBailey also writes,—
*'Ihave
had
speciesof Closteriumand
Euastrum
confinedina compressor, in water perfectly free fromotherbodies,
and
theymoved
so fastthat I founditimpossible to sketch theirhavealsoobservedthisfact,butthe
movement
always seemedto
me
of an irregularand
involuntary kind, not nearly sovigorousas that of the Diatomacese, which Professor
Max.
Schultzehasshown
to be causedby
protoplasm comingout ofand
re-enteringminuteperforationsintheshelloftheDiatom.The
mostextraordinaryphenomenon
exhibited bysome
of the Desmidieaeisthatswarming
of zoosporesmentionedabove. I have observed it inthe generaDocidium
and
Cosmarium.The
zoospores in theDesmid
appear to beendowed
with tumultuouslife,and
themotion canbe compared only totheswarming
ofbees.But
althoughthis motion has beenclaimed as a proof of animality, it has never been observed in any undisputedanimal organism, whilst it has been frequently seen in several species ofConfervoidAlgse.My
own
observa-tion extendstoa specimen of theDraparnaldia
Nana
obtainedfrom theNorth
Esk
Eiver. Imade
a note of the process atthe timewhich Iwillhere transcribe,
—
"Within each cellof the plant therewereseveral small dark vesicles interspersedthroughout the endochrome. These vesicles
moved
about.The
branches ofthe plantfellfromtheir pristine erect position asif overcome bytheweightof the endochrome, or, asif the cellwallsmightbe decaying.Then
theendochromeineach cell dividedinto two portions, withineach of which weresome
of the darkmoving
vesicles above mentioned. These twodivisions of endochromerapidly
assumed
an oval form,and
obtained a surrounding of cellulose. Presentlyeach evinced agitation as if suddenlyendowed
with life, and theycom-menced
torevolveand
beatfrom one sidetothe otherof the containingcell asif anxiousto escape. In a minute or twomore
theircell burst,and
they shot out twirling roundand
round, rushinghitherand
thitheras if in ecstasies at theirnewlyacquiredlifepower. Afterfromfive toten minutes of
thisdisplayof activelifethey
became more
soberandgraduallyassumed
a quiescentstate,some
restingsingly,but the greaternumber
aggregating." Itis a marvellous sight.You
arewatching a beautiful but inertplant; suddenly itsbranches
droop,
and
as suddenly the contents of each cellbecame
endowed
with impetuous, tumultuous, exuberantlife.Each
frondin the Desmidieae is a singlecell,and
each cellhasasuture, in
some
specieshardlyrecognisable, inotherstheconstrictionis so deep as to extend almost entirely across the
cell,the segments being joined only by a narrow isthmus
givingitthe appearance of two cells instead of one.
That
the frondisa singlecelltherecanbe nodoubt,howevermuch
21
ifan openingbe
made
inone ofthe segmentsthe contents ofbothwillescape thereout; and,moreover,
we
observe granulespassing the whole length of the frond without impediment.
A
furtherproofliesinthe conjugation of the cellsand
the formation of sporangia.The
formation of one sporangiumonlyatthe pointof contactof thetwo fronds does not accord
withthe notion of each frondhavingtwo cells.
The
multiplication of cells bj transverse divisionis fullofinterest,if only onaccountof its being theprincipal
mode
of reproduction in the protozoa.The
process is exhibited as observedbyme
ina species of Closteriumat page4, fig. 2, of the accompanyingbook of illustrations.The
fission takes place at the centre on the line of division of the twosegments, the constrictionbecoming deeper and deeper until
separationensues.
During
the process the endochrome ineachsegment gradually separates
and
assumes theposition of that in the mature plant, videfig. 2, 6.On
separation, the obtuseend becomes pointed,fig. 2, c,and
lengthens outuntilcompletedevelopment is attained.
Ithasbeen recorded that probably the Desmidiacese are
trulyreproducedonly intwo
modes
; the one bythe escape ofthe granular contents immediatelyaftertheswarming process,
and
theother bythe formation of sporangia, resulting fromthe conjugationofthe cells. Lateauthorities mentionfour:
first, cell division ; second, the retraction of contents from
parentcells
and
transformationofsame
into ciliatedzoosporesthird, division of cell contents into a
number
of zoospores;fourth, conjugation.
My
own
observationsonthe Closterium striatolatumleadme
toadd anothermode,viz., bytheforma-tion of a sporeineach segment of the frond without
conju-gation, vide illustrations, page ,figs 1, lb. Ic. Whilst in
coupling onesporanguim results fromtheconnection of two
fronds,
we
havehere two spores in each frond. Imade
alarge gathering of the C.Striatolatumthis
summer,
andfailed to findany ofthem
in a state of conjugation, although it iscommonly
observed in thisDesmid
; whilst in allthosesuffi-ciently mature, I found spores as depicted in the figures,
besides great
numbers
ofthem
in the water free from thefronds. Fig. Ic. shows the frond ruptured
and
the spore readyto passout.The
ultimate history of these spores Ishallendeavortotracethrough theensuing winterand spring.
The
universality oftheDesmidiese can be readily understoodwhen
we
find theirgerms protected in indurated spore casessuch as these.
They
may
be wafted bythe wind, or carriedby variousanimalstoanydistance,
when
meetingwithsuitableconditions they burst intolife.
Darwin
mentions fine dustpercentage of infusorialforms, fallingon boardthe " Beagle,"
when
severalhundredmilesfromany land.It is considered that those sporious bodies, called
Xan-thidium, foundinflintare sporangia of Desmids.We
havethe exactfac-simileof
them
inthe sporangiaoftheCosmarium
and
Staurastrum. Sporangiaand empty
fronds have been foundin tertiary depositsunderthebonesof extinctmammalia,
which fact furnishes us with the strongest evidence of thepowersofresistance tochangeof
some
of thesehumble and
delicate organisms.
The
uses of Desmidiese are notmuch
known.They
evolveoxygen
and
tend tokeep the waterclear inwhich theyexist.They
also formfoodfor allthe entomostracaand
many
otheranimalculse.
A
fewmonths
ago I lost a fine gathering ofClosterium ascerosum, whichI
had
putaside ina smallbottle forthepurpose of mounting,by
havingaccidentally admitted avoraciousDaphnia
pulex;and
I read that a recent observersaw
arotifer, theNotommata
myrmeleo, seize a Closteriumand
suck thewhole frond quitefree of chlorophyll.Ingiving the subjoined list of Desmidiese I
may
mentionthat there are
many
species which I have not been able to recognise, especially of the genus Closterium. Theseappar-ently
new
species I have not ventured toname.At
some
futuretimeI intend forwarding specimensand
drawings tosome
competentalgologist for identificationand
record.For
two or three years I havemade
gatherings of theDocidium
verticellatum, figuredat page2. Thisspecies has not yetbeen foundinEngland, althoughitis abundant bothon theContinent of
Europe
and
in America.My
gatheringshave beenmade
mostly from pools whichare
dug up
duringthe summer.As
they are plantswhose
favorite hauntis the open moor,
and
are taken in greatestnumbers
fromperennialponds, Ihave no doubt butthattheLake
Districtand
otherlikely placeswould
rendermany
rare,and
perhapsnew
forms.Most
of the specieshere recordedwillbe foundinthebook
of drawings. These figures aredrawn
under theCamera
Lucida,and
coloredmost
attentively after nature.A
LIST
OF
TASMANIAN
DESMIDIE^.
Closterium lunula , Closteriumsetaceum
„ striatolatum „ Ehrenbergii
Docidium
verticellatum „baculum
„ Ehrenbergii „ truncatum HegalotliecadissiliensDesmidium
SwartziiCosmarium
margaritiferum„
pyramidatum
Euastrum ansatum
Staurastrummuticum
„ dejectum
Staurastrum gracile
„ bifida
Penium
Bribisonnii „ truncatum(?) Micrasterias rotatalU.S.
Pediastrum tetras„ simplex
„ ellipticum
Aubistrodesmus falcatus