Question

Comment on the lifecycle and nature of a fern prothallus.

Answer 1

Pteridophytes show a haplo-diplontic life cycle.

Formation of spores:

The main plant body is a diploid sporophyte which contains sporophylls. The plant can be homosporous or it can be heterosporous producing haploid smaller microspores and larger megaspores.

Germination:

Germination of spores produces haploid, free-living gametophytes, called prothallus. The homosporous ferns give rise to bisexual gametophytes and heterosporous ferns give rise to separate male and female gametophytes.

Formation of gametes:

The prothallus consists of haploid male sex organ, antheridia and female sex organ, archegonia which give rise to antherozoids and eggs respectively.

Fertilisation:

Fertilisation occurs with the help of water. The diploid zygote develops into an embryo that finally forms a sporophyte.


Nature of the prothallus:

Prothallus is the free-living, multicellular, inconspicuous, haploid, photosynthetic, thalloid gametophyte of pteridophytes. It bears unicellular rhizoids for attachment to substratum. The requirement for damp and moist places is due to the requirement of water for fertilisation.