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$Selaginella$ and $Salvinia$ are considered to represent a significant step toward evolution of seed habit because
A
Megaspores possess endosperm and embryo surrounded by seed coat
B
Embryo develops in female gametophyte which is retained on parent sporophyte
C
Female gametophyte is free and gets dispersed like seeds
D
Female gametophyte lacks archegonia
Detailed Solution
$Selaginella$ and $Salvinia$ are heterosporous pteridophytes: they produce two kinds of spores, small microspores and large megaspores.
The megaspores germinate into female gametophytes, which are retained on the parent sporophyte for variable periods.
The development of the zygote into a young embryo takes place within this female gametophyte.
NCERT describes this event as a precursor to the seed habit and an important step in evolution.
There is no seed coat or endosperm in these plants, the female gametophyte is not shed free like a seed, and it does bear archegonia.
Hence the reason is that the embryo develops in the female gametophyte which is retained on the parent sporophyte.
The megaspores germinate into female gametophytes, which are retained on the parent sporophyte for variable periods.
The development of the zygote into a young embryo takes place within this female gametophyte.
NCERT describes this event as a precursor to the seed habit and an important step in evolution.
There is no seed coat or endosperm in these plants, the female gametophyte is not shed free like a seed, and it does bear archegonia.
Hence the reason is that the embryo develops in the female gametophyte which is retained on the parent sporophyte.