512 MOSSES AND FERNS chap. 



antheridia in the other groups of Liverworts. In all of the 

 homosporous Pteridophytes except the leptosporangiate Ferns, 

 however, the first division in the antheridial cell is exactly as 

 in the Anthoceroteae ; but instead of the inner cell developing 

 into a distinct antheridium, the whole of it is devoted to the 

 formation of sperm cells. It seems not improbable that this 

 type of antheridium may have been derived from that of the 

 Anthoceroteae by the suppression of the parietal cells of the 

 antheridium. 



Aside from the forms without chlorophyll, which are 

 probably all secondary, the Pteridophytes show three types of 

 gametophyte. The first, represented by most homosporous 

 Ferns, is the familiar heart-shaped prothallium, which strongly 

 recalls the simpler anacrogynous Jungermanniaceae or Dendro- 

 ceros ; the second is the lobed prothallium of Equisetum and 

 Lycopodiuin cernuum, which resembles most nearly among the 

 Hepaticae such forms as Anthoceros fusiformis ; finally, in 

 some species of Trichomanes there occur the branched fila- 

 mentous prothallia, which some authors look upon as an 

 indication of direct relationship with forms intermediate 

 betv/een Algae and Muscineae. As other species have the 

 same type of prothallium as the other Ferns, and this is always 

 true of the closely related genus HymenopJiylhnn, this view is 

 open to question. 



As far as the form and growth of the prothallium are con- 

 cerned, all forms could be traced back to the Anthoceroteae ; 

 the Fern type to forms like Dendroceros or Anthoceros Icsvis^ 

 the Equisetum and Lycopodiuin type more resembling A. 

 fusiformis. The difference in the character of the chroma- 

 tophores is a very important one, and at present must forbid 

 the assumption of any immediate connection between the 

 Anthoceroteae and existing Pteridophytes. Whether the occa- 

 sional appearance of very large plate-like chromatophores in 

 the prothallium of Osmunda cinnamomea is a reversion to a 

 primitive condition retained in the Anthoceroteae, it is, of course, 

 impossible to say, but it is not inconceivable, especially as 

 the same thing is found again normally in the sporophyte 

 of Selaginella. 



In the Anthoceroteae the origin of the archesporium is 

 different from that of the other Hepaticae, being hypodermal, 

 as in the lower Pteridophytes. The columella is in position 



