FILICES 



79 



an annulus the sporange dehisces by a fissure at right angles to it ; in 

 the Marattiacese it opens by an apical pore. The dehiscence is due to 

 unequal contraction in drying of the unequally thickened portions of 

 the cell-walls of the annulus. On one side of the sporange of a 

 considerable number of ferns are two, three, or four cells of peculiar form, 

 with lignified cell -walls, the lip-cells, between which the dehis- 

 cence always begins, and which ap- 

 pear to guide its direction. These / 

 cells together are sometimes called 

 the ' stomium.' Among the spo- 



FIG. 55. Sporange of Aspidium filix- 

 mas, showing annulus an, lip-cells 

 /c,and paraphyse attached to stalk. 

 (After Kiindig, greatly magnified.) 



ranges are frequently slender seg- 

 mented filaments, or paraphyses. 



Tn snmp PnlvnnHiarp^ thprp is FIG. 56. Development of sporange of 



OiypOQiace S a niwn Trichomanes L. s, archespore ; r, 



single (rarely more than one) out- annulus ( x 5 5>- (After Goebei.) 

 growth from the stalk of the sporange, resembling a capitate hair, and 

 sometimes septated internally. It is regarded as a paraphyse, and may 

 probably be an undeveloped sporange. The entire sorus may be 

 covered by the recurved margin of the leaf, or by a true indusium 

 belonging to the epiderm, or by a false indusium, consisting of an 

 outgrowth of the hypodermal tissue, composed of several layers of cells. 

 In Enterosora (Bak.), from British Guiana (Polypodiaceas), the sporanges 

 spring from the base of spherical chambers in the under surface of the 



