Answer:
Lignin.
Explanation:
The structural integrity of plant spores is lignin that is present in many parts of the plant. This lignin provides hardness to the plant body which help them to stand the plant erect. If this lignin is not present in the plant body the plant will not stand erected. This lignin is present in large amount in the stem of plant body so that's why the lignin provides structural integrity to plant spores
