sentences:  There are two competing theories to explain the appearance of a diplobiontic lifecycle.The interpolation theory (also known as the antithetic or intercalary theory) holds that the interpolation of a multicellular sporophyte phase between two successive gametophyte generations was an innovation caused by preceding meiosis in a freshly germinated zygote with one or more rounds of mitotic division, thereby producing some diploid multicellular tissue before finally meiosis produced spores.This theory implies that the first sporophytes bore a very different and simpler morphology to the gametophyte they depended on.