The prothallus of fern is

Physiological heterospory is seen in

The positively geotropic structure,the rhizophore of $Selaginella$,is:

Spore-bearing tracheophytes are known as:

The evolutionary advanced features of $Selaginella$ are:
$(a)$ Heterospory
$(b)$ Endosporic development of gametophyte
$(c)$ Reduced gametophyte
$(d)$ Localization of sporangium-bearing appendages in strobili
$(e)$ Unisexual gametophytes
$(f)$ Fertilization with the help of water

"Botanical snakes" are