288 



PLANT MORPHOLOGY 



ribbon, while in Trichomanes and Schizaea it is filamentous and branched, 

 resembling a moss protonema. 



The germinating spore gives rise to a short green filament and a rhizoid. 

 Soon an apical cell with two cutting faces arises and a flat thallus develops. 

 Then an apical cell with three cutting faces is formed and the median por- 

 tion of the prothallium becomes slightly thickened, the wings remaining 



B 



Fig. 243. Development of the sporangium of Cyrtomium fakatum (Polypodiaceae), X400. 

 A, young stage, showing tetrahedral apical cell cutting off segments to form a stalk; B, 

 formation of cap cell and primary sporogenous cell; C, anticlinal division of cap cell; D, 

 formation of first tapetal cell from primary sporogenous cell ; E, completion of tapetum ; 

 F and G, later stages, the tapetum becoming two-layered; H, breaking down of tapetum 

 and rounding off of spore mother cells. 



one-layered. Eventually a group of initials is formed in the apical notch, 

 replacing the apical cell. 



In most of the Filicales the prothallium is monoecious, the sex organs 

 arising from the ventral surface. The antheridia appear at a very early 

 stage, often w^hen the prothallium is still filamentous, and continue to be 

 produced for a long time. The first antheridia are often marginal as well 

 as ventral in position. Later they become irregularly scattered over the 

 entire ventral surface. The antheridia are not embedded in the prothal- 

 lium but project beyond its surface. 



