sentences:  This explains the behaviour of some algae, such as "Ulva lactuca", which produce alternating phases of identical sporophytes and gametophytes.Subsequent adaption to the desiccating land environment, which makes sexual reproduction difficult, might have resulted in the simplification of the sexually active gametophyte, and elaboration of the sporophyte phase to better disperse the waterproof spores.The tissue of sporophytes and gametophytes of vascular plants such as "Rhynia" preserved in the Rhynie chert is of similar complexity, which is taken to support this hypothesis.