594 



MOSSES AND FERNS 



CHAP. 



ies resembling the oil bodies of Liverworts are also met with in 

 this genus. The sexual organs closely resemble those of the 

 Polypodiaceae, but the antheridia have a well-marked stalk, 

 something like that found often in the Hymenophyllacese. 

 Among the many genera and species aside from these, while 

 there is extraordinary variety, the differences are all of second- 

 ary importance, and consist mainly in the form and venation of 

 the leaves and the position of the sporangia. The leaves range 

 from the undivided ones of Vittaria or Scolopendrhim to the 



Fig. 22,2. — Platy cerium alcicorne. A, Whole plant, much reduced; B, tip of a spo- 

 rophyll, showing the crowded sporangia. (A, after Coulter; B, after Diels.) 



repeatedly divided leaves, usually pinnate, of such forms as 

 Pteris aquilina. In some tropical epiphytic species, such as 

 Asplenium nidus, Platy cerium, species of Poly podium, the 

 leaves are arranged so that they form receptacles for collecting 

 humus. In the two latter genera these leaves are very much 

 modified, the two forms of leaves being familiar to all botanists 

 m the common Platycerium alcicorne, where the closely over- 

 lapping round basal ones are very highly developed. 



