What is the shape of the strobili or cones in Pteridophytes?

Which pteridophyte is called as horse-tail?

Cambium is absent in ..........

In which one of the following species of $Selaginella$,the apex continues its vegetative growth beyond the formation of $strobilus$?

In which of the following plants is the gametophytic phase secondary?

Ovules are absent in ...........