ANTHOCEROTEAE. 



157 



the Alga when quite young, a nostoc-filament forcing its way through the cleft into the 

 mucilage-cavity. This is followed by a rapid process of division in the surrounding 

 cells, and the cleft closes. But the parietal cells of the cavity grow out, in pro- 

 portion as the Nostoc increases, into tubes which come into close contact with the 

 Nostoc, and as they multiply and divide they look like a parenchymatous tissue with 

 Nostoc settled in its intercellular spaces. ( Compare Blasia^) The species t& Anthoceros 

 are monoecious ; the antheridia and archegonia are not placed as a rule in any fixed 

 relative order. The antheridia are always at first in perfectly closed cavities, which in 

 Dendroceros rise like bladders above the surface of the thallus, but in our native 

 species of Anthoceros and in Notothylas are entirely sunk in the thallus. It is not till 

 the chlorophyll-corpuscles in the walls of the antheridia have turned yellow and 

 the spermatozoids are mature that the covering is rent, and the antheridia open at their 

 apex and discharge their contents. 



The development of the archegonia is in all important points the same as in the 



a 



FIG. 106. Longitudinal section through the apex 

 of a thallus of Anthoceros with archegonia. After 

 Leitgeb. 



FlG. 107. Longitudinal section of a young sporogonium of Anthoceros 

 laevfs; L the involucre. After Hofmeister, magn. 150 times. 



rest of the Hepaticae ; only the mother-cell remains sunk in the tissue of the thallus, 

 and hence the neck does not project above the thallus even when the archegonium is 

 fully formed (Fig. 106). 



The development of the sporogonium has already been described as differing from 

 that of the other Hepaticae. While the embryo becomes a multicellular body broader 

 at its base, the surrounding tissue of the thallus divides repeatedly and grows up into 

 an overarching involucre, which is afterwards pierced through by the elongating 

 sporogonium. Cells which remain sterile and form a connected net-work are separated 

 off from the archesporium. In Dendroceros and some foreign species these sterile 

 cells are elaters composed of a row of cells and traversed by a broad brown spiral 

 band. The cells of the foot are prolonged into tubes which penetrate into the 

 adjoining tissue. The sporogonium elongates and forms a narrow capsule which in 

 some European species is from fifteen to twenty millimetres in height ; its brown wall 

 opens from above downwards into two valves and its epidermis has stomata. The 

 prolonged intercalary growth at the base of the sporogonium is characteristic of this 



