Lesson 8 of 12 · 5 min
Homospory, heterospory and the seed habit
NCERT §3.3
At the field station a microscope shows spores from two plants. The fern's spores are all alike. The Selaginella slide has a few huge spores and a crowd of tiny ones.
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In short
Most pteridophytes make spores of only one kind; they are homosporous.
Selaginella and Salvinia make two kinds: large megaspores (macrospores) and small microspores. They are heterosporous.
Megaspores grow into female gametophytes and microspores into male gametophytes.
In heterosporous plants the female gametophyte stays on the parent sporophyte for a variable time, and the zygote grows into a young embryo inside that female gametophyte.
This is a forerunner of the seed habit, which is regarded as an important step in evolution.