Hornworts

Anthoceros is an example of a hornwort. The life cycle with regard to alternation of generations is much like that of Marchantia. One interesting difference, however, is that each cell of the gametophyte has only one chloroplast, and each chloroplast possesses pyrenoids similar to those of green algae. Again, the sporophyte grows on the gametophyte, the gametophyte being the conspicuous generation. But then a special development takes place. The spore-producing tissue forms a long cylinder parallel to the axis, and the spores mature from the top down. The foot of the sporophyte, which is anchored to the tissue of the gametophyte, grows downwardly and through the gametophyte tissue to penetrate the soil beneath. While one may infer that this represents a harbinger of independence in the sporophyte generation and, thus, a step toward the higher plants, this inference is probably without sufficient basis. It is more likely that Anthoceros, rather than being an ancestor of higher forms, is a dead end.