86 VASCULAR CRYPTOGAMS 



Order 4. — Hymenophyllace^. 



The oophyte generation is known but in a very few species of 

 HymenophyllaceEe, Where it has been observed (some species of 

 Hymenophyllum and Trichomanes) it differs from that of other ferns, 

 and is usually filiform, closely resembling the protoneme of a moss, but 

 somewhat coarser. Antherids appear to be produced aX the middle of 

 these filaments, and archegones at their extremity. But apogamy is 

 much more common in the Hymenophyllaceae than in any other family 

 of ferns, and it is doubtful whether it does not even occur regularly in 

 some species. Bulbils or gemmae are produced abundantly on the pro- 

 thallium, consisting of a small number of cells, and borne on pedicels 

 or sterigmas. They germinate with extreme slowness. In Trichomanes 



pyxidiferum (L.) the prothallium is 



ar^ -;:s=^st£p^ frequently an aposporous growth, 



derived from imperfect arrested 

 sporanges, or even from cells of 

 the placenta. The archegones 

 are borne on peculiar structures, 

 known as archegoniophores^ mas- 

 sive outgrowths of the prothal- 

 lium, each archegoniophore bear- 

 ing either a single archegone or 

 several. The archegoniophore is 

 usually a multicellular structure. 



Fig. 61.— Archegoniophore of Trichomanes pyxi- and the VentCrS of the archegOnCS 

 di/erum L., bearing five archegones, ar. of .,-,,.. . rr^ 



different ages (x 175). (After Bower.) are imbedded in Its tissue. T. 



alatum (Sw.) is habitually apo- 

 gamous, and is possibly never reproduced sexually. Aposporous pro- 

 thallia spring in great numbers from all parts of the frond, often quite 

 independent of the sori, and are more flattened and ribbon-Uke in struc- 

 ture than those of most Hymenophyllacese. They produce large 

 numbers of stalked gemmae. Archegones have never been observed in 

 this species, and the antherids are imperfect, and apparently functionless 

 The spores are multicellular before germination. The archegones differ 

 from those of other ferns in having a perfectly straight neck. 



The sporanges have a complete horizontal or oblique annulus 

 (incomplete in Loxsoma, R. Br.), and hence dehisce by a vertical fissure. 

 They are borne on a prolongation of the fertile vein, the columel, which 

 projects beyond the margin of the leaf, and is enclosed in the cup-shaped 

 indusium. The columel or placenta elongates by intercalary growth, 

 and the sporanges are produced on it iii a spiral line in basifugalsucces- 



