XXII] 



GAMETOPHYTE 



171 



branches peculiar swollen cells, having pale chromatophores, and fungal 

 infection; from these rhizoids spring (Fig. 457). This suggests mycorhizic 



Fig. 457. A =3. prothallus of Schizaea pusilla, bearing spherical cells {s) with endophytic fungal filaments: 

 rtr="archegonia: a;/ =antheridia. ^=: segmentation of an antheridium of Schizaea rii}estris\ the lid is not 

 always divided. C, /) = mature antheridium and archegonium of Schizaea pusilla. {A, C, /) after Britton 

 and Taylor. B after von Goebel.) 



nutrition. The antheridia and archegonia are solitary and distal on special 

 branches. These prothalli, so different from the ordinary type, do not assume 

 the filamentous form as a direct consequence of growth under diminished 

 intensity of light, though this is the effect on many ordinary prothalli. Nor 

 does exposure to stronger light induce them to take a flattened form. As 

 Goebel remarks: "they are blind — they persist in a state which in related 

 forms under favourable conditions exists only as a juvenile stage rapidly 

 passed over." They are in point of fact the simplest prothalli known among 

 the Pteridophyta. They suggest a primitive state, and provoke comparison 

 with green Algae. 



The archegonia are of the ordinary Leptosporangiate type, but with 

 straighter necks, a feature of primitive Ferns. The antheridia are peculiar in 

 having their first segmental wall flat instead of funnel-shaped, which accords 

 with the filamentous stalk in Schizaea, and it is retained in Anemia. There 

 is, however, another feature which differentiates Lygodium from the rest of 

 the Family. Schlumberger states that in its antheridium the cap-cell is 

 divided, as it habitually is in the most primitive Ferns: and one of the 

 resulting cells is thrown off on dehiscence {Flora, p. 396, 1911). This 

 apparently trivial feature acquires importance as occurring in the antheridium: 

 for its complexity follows that of the sporangium (Vol. I, pp. 290-292). 

 Here Lygodium, which has the larger sporangium and spore-output, has 



