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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 vegetable

king-dom.

They

haveattractedattentionnot only on account of thestrikingbeauty

and

variety of their forms, but also

by

reason ofthedoubtas to their position,whetherintheanimal

or vegetable kingdom, having caused considerable discussion

amongst

learnedalgologists.

They

are

now

almost univers-ally assigned to the vegetable kingdom.

The

presence of starch in the ludochrome,

and

their

mode

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 increase

by

voluntary division ; third, the definite organ, possessed

by

some

genera, inwhich active molecules appear to enjoy

an

independentmotion,

and

theparietiesofwhich appearcapable of contracting

upon

itscontents; fourth, the

swarming

motion

which takesplace at a certain stage of their growth. Other arguments have been advancedin support of this side ofthe

question,

and

Ehrenberg

went

so far as to describe orifices,

havingprotruding organsor feet immediately behind them,

thebasisof such organs being the

moving

molecules which

are 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

powerofmotion

and

increase

by

self-divisionhave

now

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,theone

side of whichisexposedto thesun's rays,

we

shallfind,after

a shorttime, thatmostof

them

have found their

way

to the illuminated sideof the glass. ProfessorBailey also writes,

*'Ihave

had

species

of Closteriumand

Euastrum

confinedin

a compressor, in water perfectly free fromotherbodies,

and

they

moved

so fastthat I founditimpossible to sketch their

(2)

havealsoobservedthisfact,butthe

movement

always seemed

to

me

of an irregular

and

involuntary kind, not nearly so

vigorousas that of the Diatomacese, which Professor

Max.

Schultzehas

shown

to be caused

by

protoplasm comingout of

and

re-enteringminuteperforationsintheshelloftheDiatom.

The

mostextraordinary

phenomenon

exhibited by

some

of the Desmidieaeisthat

swarming

of zoosporesmentionedabove. I have observed it inthe genera

Docidium

and

Cosmarium.

The

zoospores in the

Desmid

appear to be

endowed

with tumultuouslife,

and

themotion canbe compared only tothe

swarming

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

obtained

from theNorth

Esk

Eiver. I

made

a note of the process at

the timewhich Iwillhere transcribe,

"Within each cellof the plant therewereseveral small dark vesicles interspersed

throughout 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 were

some

of the dark

moving

vesicles above mentioned. These two

divisions of endochromerapidly

assumed

an oval form,

and

obtained a surrounding of cellulose. Presentlyeach evinced agitation as if suddenly

endowed

with life, and they

com-menced

torevolve

and

beatfrom one sidetothe otherof the containingcell asif anxiousto escape. In a minute or two

more

theircell burst,

and

they shot out twirling round

and

round, rushinghither

and

thitheras if in ecstasies at their

newlyacquiredlifepower. Afterfromfive toten minutes of

thisdisplayof activelifethey

became more

soberandgradually

assumed

a quiescentstate,

some

restingsingly,but the greater

number

aggregating." Itis a marvellous sight.

You

are

watching a beautiful but inertplant; suddenly itsbranches

droop,

and

as suddenly the contents of each cell

became

endowed

with impetuous, tumultuous, exuberantlife.

Each

frondin the Desmidieae is a singlecell,

and

each cell

hasasuture, in

some

specieshardlyrecognisable, inothersthe

constrictionis 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,however

much

(3)

21

ifan openingbe

made

inone ofthe segmentsthe contents of

bothwillescape thereout; and,moreover,

we

observe granules

passing the whole length of the frond without impediment.

A

furtherproofliesinthe conjugation of the cells

and

the formation of sporangia.

The

formation of one sporangium

onlyatthe pointof contactof thetwo fronds does not accord

withthe notion of each frondhavingtwo cells.

The

multiplication of cells bj transverse divisionis fullof

interest,if only onaccountof its being theprincipal

mode

of reproduction in the protozoa.

The

process is exhibited as observedby

me

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 two

segments, the constrictionbecoming deeper and deeper until

separationensues.

During

the process the endochrome in

eachsegment 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 outuntil

completedevelopment is attained.

Ithasbeen recorded that probably the Desmidiacese are

trulyreproducedonly intwo

modes

; the one bythe escape of

the granular contents immediatelyaftertheswarming process,

and

theother bythe formation of sporangia, resulting from

the conjugationofthe cells. Lateauthorities mentionfour:

first, cell division ; second, the retraction of contents from

parentcells

and

transformationof

same

into ciliatedzoospores

third, division of cell contents into a

number

of zoospores;

fourth, conjugation.

My

own

observationsonthe Closterium striatolatumlead

me

toadd anothermode,viz., bythe

forma-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. I

made

a

large gathering of the C.Striatolatumthis

summer,

andfailed to findany of

them

in a state of conjugation, although it is

commonly

observed in this

Desmid

; whilst in allthose

suffi-ciently mature, I found spores as depicted in the figures,

besides great

numbers

of

them

in the water free from the

fronds. Fig. Ic. shows the frond ruptured

and

the spore readyto passout.

The

ultimate history of these spores I

shallendeavortotracethrough theensuing winterand spring.

The

universality oftheDesmidiese can be readily understood

when

we

find theirgerms protected in indurated spore cases

such as these.

They

may

be wafted bythe wind, or carried

by variousanimalstoanydistance,

when

meetingwithsuitable

conditions they burst intolife.

Darwin

mentions fine dust

(4)

percentage of infusorialforms, fallingon boardthe " Beagle,"

when

severalhundredmilesfromany land.

It is considered that those sporious bodies, called

Xan-thidium, foundinflintare sporangia of Desmids.

We

have

the exactfac-simileof

them

inthe sporangiaofthe

Cosmarium

and

Staurastrum. Sporangia

and empty

fronds have been foundin tertiary depositsunderthebonesof extinct

mammalia,

which fact furnishes us with the strongest evidence of the

powersofresistance tochangeof

some

of these

humble and

delicate organisms.

The

uses of Desmidiese are not

much

known.

They

evolve

oxygen

and

tend tokeep the waterclear inwhich theyexist.

They

also formfoodfor allthe entomostraca

and

many

other

animalculse.

A

few

months

ago I lost a fine gathering of

Closterium ascerosum, whichI

had

putaside ina smallbottle forthepurpose of mounting,

by

havingaccidentally admitted avoracious

Daphnia

pulex;

and

I read that a recent observer

saw

arotifer, the

Notommata

myrmeleo, seize a Closterium

and

suck thewhole frond quitefree of chlorophyll.

Ingiving the subjoined list of Desmidiese I

may

mention

that there are

many

species which I have not been able to recognise, especially of the genus Closterium. These

appar-ently

new

species I have not ventured toname.

At

some

futuretimeI intend forwarding specimens

and

drawings to

some

competentalgologist for identification

and

record.

For

two or three years I have

made

gatherings of the

Docidium

verticellatum, figuredat page2. Thisspecies has not yetbeen foundinEngland, althoughitis abundant both

on theContinent of

Europe

and

in America.

My

gatheringshave been

made

mostly from pools which

are

dug up

duringthe summer.

As

they are plants

whose

favorite hauntis the open moor,

and

are taken in greatest

numbers

fromperennialponds, Ihave no doubt butthatthe

Lake

District

and

otherlikely places

would

render

many

rare,

and

perhaps

new

forms.

Most

of the specieshere recordedwillbe foundinthe

book

of drawings. These figures are

drawn

under the

Camera

Lucida,

and

colored

most

attentively after nature.

A

LIST

OF

TASMANIAN

DESMIDIE^.

Closterium lunula , Closteriumsetaceum

„ striatolatum „ Ehrenbergii

(5)

Docidium

verticellatum „

baculum

„ Ehrenbergii „ truncatum Hegalotliecadissiliens

Desmidium

Swartzii

Cosmarium

margaritiferum

pyramidatum

Euastrum ansatum

Staurastrum

muticum

„ dejectum

Staurastrum gracile

„ bifida

Penium

Bribisonnii „ truncatum(?) Micrasterias rotata

lU.S.

Pediastrum tetras

„ simplex

„ ellipticum

Aubistrodesmus falcatus

References

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