Pteridophytes are characterized by

In $Pteris$,the sori are

Microphyllous leaves are produced in

Indusium in $Pteridium$ is:

In some of the pteridophytes and gymnosperms,the sporophylls aggregate at the apices of the main stem or its branches to form definite compact structures. These compact structures are called:

Which of the following is not involved in the fertilization of a fern?