Which one of the following is considered important in the development of seed habit?

Heterospory is the production of spores of two different sizes and of two different developmental patterns. Heterospory is an expression of sex determining spores of the plant. It is the most important evolutionary development in the vascular plants because it has ultimately lead to seed development, $\mathrm{eg}$, Selaginella, Sabvinia, Azolla, etc.