Question

What is heterospory? Briefly comment upon its significance. Give examples.

Answer 1

This is often considered to be a prerequisite to seed formation, where two different sorts of spore forms additionally to the present the seed plants show the certain characteristics that have led to the formation of the seed.

Complete step by step answer:
Heterospory
- The microsporangia possesses microsporangia whereas megasporangia contain megaspores in them. Each microsporangium contains an outsized number of microspores whereas each megasporangium possesses usually only four megaspores. The condition of the assembly of two sorts of dissimilar spores,differing in shape and size within the same species is termed heterospory.
- When one quiet spores are present, viz., Equisetum and ferns, the condition is named homospory.
- The microspores develop male female gametophytes which can even be called as microgametophytes and megagametophytes.
- The origin of seed habit is related to the subsequent important prerequisites :
The production of two sorts of spores i.e., heterospory.
The retention and germination of the fertilization of the egg and embryo formation which remains within germinating megaspore.
Development of just one megaspore per megasporangium.
Significance of heterospory
- The differentiation of microspores and megaspores and their dependence upon the sporophyte has some advantages.
- The condition of heterospory in selaginella constitutes one among the vital phases within the evolution of the plants.
The phenomenon of heterospory is of great biological advantage thanks to the very fact that an outsized megaspore which contains female gametophyte derives its food the sporophyte, and is independent of the external conditions as might interfere with the expansion of a life style gametophyte.
Examples of heterospory
- The heterospory is observed in seven genera- Selaginella, Isoetes, Marsilea ,Salvinia, Azolla, Regnellidium and Pilularia.
- In certain species of selaginella just one megaspore develops within the megasporangium.
- The highest evolved species, that is, S. apoda has advanced almost upto the rank of a spermatophyte.
- The megaspore remains within the sporangium; it itself fertilizes and in such how for the primary time the gametophyte of selaginella shows complete dependence of the gametophyte upon sporophyte as in angiosperms.

Note:
- The sporangia show greater specialization than those of ferns as they're differentiated into micro and megasporangia.
- In the case of homospory the sex are often differentiated only at the gametophyte stage, but here the sex could also be differentiated even at the saprophytic stage by the presence of small and enormous sized microspores which form antherozoids and eggs respectively.