BOTANY,Degree 01H/Sub.,BRYOPHYTA :General Introduction.Dr.Dilip Kumar Jha (Lecture series 19 ).

● Bryophytes are the simplest and first among terrestrial (land inhabiting) plants .

● They are non ‐vascular,non ‐flowering and non‐seeded.

● They are the first embryophytes (zygote develops into embryo ),first archegoniate (female sex organ is archegonium) which occupy an intermediate position between thallophyta (algae ) and pteridophyta.

● In bryophytes mechanical tissue are absent . Sex organs are stalked , multicellular and covered by single layered sterile jacket.

● In Bryophytes vascular tissue (xylem and phloem ) is absent. Thus, they are also called atrcheata.

● Bryophyta is a small group of plants including about 24000 species under 800 genera.

Distribution and Habitat of Bryophytes

● Bryophytes are cosmopoliton in distribution .They are present in tropical and subtropical forests upto arctic region, upto height of appx 20000 feet on mountains.

● Bryophytes are probably not present in sea and antarctica.

● Bryophytes are terrestrial .They complete their vegetative phase on land but water is necessary for their reproduction.Thus,they are called amphibians of the plant kingdom.

● Bryophytes generally grow in moist and shady places eg.moist rocks,moist ground, tree trunks etc.Species of Sphagnum grows in boggy and marshy conditions.

● Some bryophytes are aquatic eg.Riccia fluitans,Ricciocarpus natans.Riella completes its life cycle fully under water.

● Some bryophytes grow as epiphytes on trunk of other plants eg.Dendroceros,Porella .

● Polytrichum juniperum,Tortula desertorum are some xerophytic

bryophytes.

● Radula protensa grows on the fronds of fern ( epiphyllous ).

● Bryophytes are generally autotrophic.But,Buxbaumia aphylla and Cryptothallus mirabilis are saprophytic

PLANT BODY OF BRYOPHYTE

● Bryophytes are first among the plant kingdom to show heteromorphic alternation of generation I.e. there are two phases in the life cycle which are morphologically distinct.The dominant phase is represented by a haploid (n ),free living nutritionally independent GAMETOPHYTE to which physically and nutritionally dependent diploid (2n ) SPOROPHYTE is attached.The sporophyte is partially or fully parasitic upon gametophyte.

A. GAMETOPHYTE

• This is the dominant plant body which develops from haploid spores.

• There are two forms of gametophyte: thallose and erect ( foliose ).

• The thallose forms are prostrate and without the differentiation of root,stem and leaves eg. Riccia,Marchantia Anthoceros etc.

• Erect forms have leafy axis.The erect or foliaceous forms pass through a temporary filamentous stage called protonema eg Plytrichum,Sphagnum,Funaria etc.

• There is complete absence of true roots.But ,in both thallose and foliose forms anchorage and absorption of gametophyte are helped by uni (Riccia,Marchantia ) or multicellular rhizoids (Funaria ) attached to the lower side of gametophyte.

• The lower surface of thallose forms also possesses multicellular scales.Scales protect the growing points.Scales are absent in aquatic forms.

• The gametophyte reproduces by both vegetative and sexual methods.

• There are different methods of vegetative reproduction viz by death and decay of older parts, by the formation of adventitious branches,by gemmae,by branch tip, by bulbils,by protonema,by rhizoids,by tubers etc.

• Sexual reproduction in bryophytes are highly oogamous type.It takes place by the fusion of biflagellate,motile male gamete called antherozoids or sperm with non motile female gamete or egg which is retained within the female sex organs.

• Gametes are produced in complex,multicellular,stalked and jacketed sex organs.

• Male sex organ is called antheridium and the female sex organ as archegonium.

• In monoecious spp. Both sex organs develop on the same plant eg. Funaria hygrometrica whereas in dioecious forms male and female sex organs develop on separate plants eg . Marchantia.

• The sex organs are attached to upper surface of the thallus in thalloid forms.

• The antheridium is ellipsoidal or club shaped stalked structure.It is made up of a single celled sterile jacket layer which encloses a central mass of androcyte mother cells.Each of these cells divide mitotically to produce two squarsh or cubical androcytes.Each androcyte gives rise to a single male gamete also called antherozoids or sperms.Each sperm usually consists of minute,slender,spirally curved body furnished with two whiplash type flagella which are long and borne terminally.

• The archegonium is a flask shaped structure.It consists of two portions.The upper portion is slender and eloongated.It is called neck.The neck consists of one to many Neck Cana Cell .The lower portion is swollen and sac like.It is called venter.The venter is made up of 1 or 2 layers thick wall of sterile cell.The venter encloses larger egg cell and smaller ventral canal cell just above the venter.

• During fertilization the antheridium ruptures at its apex.The sperms are liberated.The liberated sperms swim in water and reach the archegonium.One sperm fuses with egg to form diploid zygote.

• With the formation of zygote,the gametophytic generation ends and sporophytic generation starts.

B. SPOROPHYTE

• Zygote is the beginning of the sporophytic generation. Zygote is not independent from gametophyte.

• Zygote does not undergo any resting period.It after segmentation develops into a multicellular ,undifferentiated embryo within the venter

• The multilayered venter meant for protecting the young embryo is called calyptra.

• The embryo by further segmentation and differentiation develops into a lefless and branchless sporophyte also called sporogonium.

• The sporophyte remains attached to the gametophyte throughout its life.

• Thus,sporophyte is completely ( Riccia ) or partially dependent upon gametophyte.

• The sporophyte may or may not be differentiated into foot,seta and capsule.

• The capsule is partially sterile and partially fertile.

• The diploid Spore Mother Cells inside the capsule undergo meiosis to produce haploid spores arranged in tetrad.

• The haploid spores again represent the start of gametophytic generation.

• The spores are liberated either by death and decay of capsule wall or by specific pore or valve.

• The spores in many genera are liberated by spirally thickened sterile hygroscopic cells elaters (Marchantia ) or elaterophores (Pellia ) or teeth like structure called peristome ( Funaria ).

• The elaters develop from diploid cells of capsule.On maturity they become dead.

• After liberation from the capsule the spores directly or indirectly gives rise to gametophytic plant.

• In bryophytes there is progressive sterilization of sporogenous tissue as one moves from lower to higher forms.

• There is distinct alternation of generation in bryophytes.Gametophytic phase starts with the formation of haploid spores and ends with the formation of sperms and egg.Sporophytic phase starts with the formation of diploid zygote after fertilization.It ends with the formation of haploid spores by meiosis in diploid Spore Mother Cells.

ECONOMIC IMPORTANCE OF BRYOPHYTES: 1 Sphagnum is chief constituent of peat.It is used as fuel,in preparation of ethyl alcohol,peat tar,paraffin etc.

2 Peat has the capacity to retain water for long period.Thus it is used to cover plants root during transportation.,tie the grafts and as seed bed and packing materials.

3. Some moss after death help in soil formation.

4 Act as soil binder.

5 Some bryophytes are used as fodder.

6 Some bryophytes act as acid indicator of the soil.

Figure showing gametophytic thallus of thalloid form. Figure showing gametophytic plant of erect form.

Figure showing an antheridium.

Figure showing an archegonium.