Get complete information on the Reproduction in Pteridophytes

(A) Vegetative (B) Sexual.

(A) Vegetative reproduction:

It is of rare occurrence and may take place by fragmentation as in S. rupestris. The prostrate branches develop roots and break into small fragments each developing into a new plant. Certain species of Selaginela propagate by bulbils or by smaller tubur as in S. chrysocaulos and S. chrysorrhizos. In the former case the tubers are formed at surface of the ground and are called surface tubers. In the latter case they are developed underground hence called underground tubers.

In Dryopteris adventitious buds arise in the axil of leaves and are detached from the plant and form new plants.

(B) Sexual Reproduction:

The reproductive structure is a compact one is Selaginella and develops at the terminal portions of branches. It is called strobilus or spike and is a sessile structure. The strobilus is either erect or horizontal. It tapers towards the apex and the length varies from A of an inch to inches. In some cases the strobili owing to the loose arrangement of sporophylls become, inconspicuous.

A strobilus posseses many liguate sporophylls arranged in the form of cluster, each bearing on its upper side and near its base a small short stalked sporangium. The sporangia, instead of being all alike, are of two distinct kinds. One type of sporangia contains four large spores and the other contains many small spores.

The large spores are megaspores and the sporangium which bears them is the megasporangium borne on a megasporophyll. Similarly the small spores are microspores formed in microsporangium borne on a microsporophyll. Each sporophyll, like the leaf has got a ligule in its axil. The dimorphic condition is known as heterospory.

For fertilization, usually the male gametophytes are shed from the microsporangium on the ground at 13-celled stage. Some of microgametophytes shift down between the sporophylls and may fall into the partly opened microsporangia. Now-lying in the megasporagium, the two kinds of gametophyte complete their development. If sufficient water is present, fertilization takes place.

The young embryos develop within the wall of megasporangium and drop out as soon as they develop a root and primary shoot. Later on the openings of the megasporangium becomes wider and the megagametophyte with their developing embryos fall on the ground.

This is specially significant since it introduces in the life cycle a close parallel to the pollination and seed formation habits found in the spermatophytes. Therefore, when the megaspore with its newly formed embryonic sporophite falls to the ground, it is for all practical purposes a seed and hence Selaginella approaches the seed habit. The oosphere after fertilization gets surrounded by a wall and becomes oospore.

After divisions oospore develops, into embryo or sporophyte. In fern also sexual reproduction takes place through spores which are borne is sporangia. When the leaves are mature they bear groups of sori on the undersurface of fertile pinnae.

Such fronds are called sporophylls. The sori are borne in two rows on two sides of median vein of a pinnule in between the margin and the midrib. Each sorus is covered by a kidney shaped indusium covering the sorus. In the centre of the sorus the vein ends in a placental tissue from which a number of sporangia arise without any order of development.

Each mature sporangium has a long slender multicellular stalk and number of spores enclosed in the capsule wall may be 64 or less. When capsule is mature and dry, spores are thrown out. All the entire sporangium develops from a single initial cell and the development of sporangium is leptosporangiate type.

Spores are homosporus i.e. similar and under suitable conditions give rise to gametophyte which bears antheridium and archegonia. Antherezoids are produced in antheridium and are large spirally coiled and bears numerous large flagella. Archegonium is flask shaped and contain egg, ventral canal cell and neck cancel cell. Venter encloses egg (oosphere) and ventral canal cell.

Neck canal cell has two nuclei in fern. During fertilization, ventral canal cell and neck canal cell along with the tip of neck disintegrate and the neck forms a canal like passage full of mucilage and some chemicals like malic acid. These chemicals attract antherozoids and one of male gametes fuses with the oosphere forming a diploid oosphere. Although there are several archegonia in the prothallus, only one is fertilized. The oospore formed gives rise to embryo or sporophyte and usually one sporophyte is developed out of a gametophyte.

Division 4 -> Spermatophyta:

(i) These are vascular plants bearing seeds.

(ii) Secondary growth is present in most members.

(iii) The sporophyte is conspicuous plant in the life cycle.

(iv) This division contains subdivisions Angiosperms & Gymnosperms.