IX THE POLYPODIACEAE 



3 



to 



second cell there was cut oft" laterally a cell which developed im- 

 mediately by longitudinal and transverse divisions into an ex- 

 panded branch with a definite growing region at the apex. 

 The third cell of the original filament divided by a longitudinal 

 division into two cells, a larger and a smaller one. From the 

 larger of these two cells a branch developed which formed another 

 expanded prothallium whose growing point was not definitely 

 marked. In the meantime the growth of the primary prothallium 

 had continued and an expanded part was formed showing a 

 decided tendency to branch dichotomously at the apex. 



Fig. 10. A, B. Branched prothallia of Asplenium bidbiferiim Forst. 

 C. Branched prothallium of Asplenium platyneuron (L.) Oakes, X 75- 



X 7: 



Asplenium platyneuron (L.) Oakes. — Fig. io, C, shows a pro- 

 thallium of this species which developed in a crowded region on a 

 soil culture. In this case branching occurred at a later period in 

 the development of the prothallia. No filament was formed in 

 the early development of the prothallium, but the second cell by 

 division gave rise immediately to the beginnings of an expanded 

 cell plate which during development branched dichotomously. 

 Each branch in turn formed a distinct growing region at its apex. 



