Chapter 21, Problem 26A

Summary Introduction

To write:

The advantage of fern sori being in the under surface of fronds rather than on the upper.

Introduction:

Pteridophytes are the seedless vascular plants with about 13000 species. They have sporophytic plant body, inconspicuous gametophytes containing small sessile antheridia and partially embedded erchegonia with 4-rowed neck.

Explanation of Solution

The most conspicuous of the pteridophytes are the ferns. The plant body is a sporophyte. It is differentiated into true leaves, stem, and roots. Leaves are large and are known as fronds. Ferns are pteridophytes that bear sporangia in sori on the leaves which show circinate ptyxis in the young condition. Sporangia spread along all of the veins of the lower surface of the fertile frond. This presumably confers some survival advantages on the germinating prothallus.

Conclusion

Thus, the fern sori grows on the under surface of fronds to protect them from the external injury.