A hypothetical account for the emergence of a sporophyte generation during the evolution of vascular plants. It postulates that early plants were exclusively haploid gametophytes. At some point a zygote ‘germinated’ mitotically instead of meiotically, producing a rudimentary diploid sporophyte. Hence, a sporophyte generation was ‘inserted’, or interpolated, into the life cycle. The sporophyte evolved to become increasingly elaborate and the more prominent form—as in modern seed plants—while the gametophyte became progressively reduced. Compare transformation hypothesis.