2 Transactions. 



Sexual Generation. 



"^The spores of the four tree-ferns studied all germinated 

 very quickly — in two or three weeks (fig. 52). The slits of 

 ■dehiscence were generally very narrow, and the spore-case re- 

 mained attached. The normal heart-shaped prothallium was 

 rapidly attained, and was similar in form and development to 

 that of the Polypoiiaceai. But the tree-ferns' prothallium ex- 

 hibits excessive variability. The apical cell may arise (especially 

 in Dicksonia) in the cell next to the spore (fig. 57), or a long 

 filament be formed ; or even after the apical cell is formed it 

 may grow out into a filament (fig. 62). In well-nourished 

 prothallia, after about seven segments have been cut off, by a 

 vertical pericline in the apical cell a three-sided initial is cut 

 out, and a small - celled meristem now comes to occupy the 

 depression at the apex. Normal prothallia produce a few 

 antheridia and then archegonia on the " cushion." " Ameristic " 

 prothallia, as usual in ferns, produce antheridia only. 



The prothallia (of Dicksonia especially) produce adventi- 

 tious " shoots " very readily if conditions are unfavourable. 

 Filiform upright branches spring especially from the margins 

 of male prothallia, and produce abundant antheridia. In a few 

 cases one of these " shoots " formed an apical cell and formed a 

 normal prothallium. 



Antheridia. 



All the forms examined were similar in the structure of 

 the complex normal type of antheridium and in the variety of 

 the reduction forms. 



Normal Development. 



(a.) Rudiment: lighter green, and more de.ise'.y protoplasmic, (b.) Gap 



cell, (c.) Upper ring cell, (d.) Lower ting cell, (e.) Pedicil. 



In Dicksonia an opercular cell was often cut out from the 

 cap cell, and the ring cells were sometimes divided. In the re- 

 duced antheridia few walls are formed. 



Ausknce of Pedicel. 



