STRUCTURE OF FERN'S 



i::: 





indusium. This iiulusium separates from the frond at 

 its edges, and the sporangia are exposed. Not all ferns 

 have imlusia. The polypode (Figs. 

 30G, 307) does not: the sori are 

 naked. In the brake (Fig. 308) and 

 maiden-hair (Fig. 309) the edge of 

 the frond turns over and forms an 

 indusium. In some ferns (Fig. 310) 

 an entire frond becomes contracted 

 to cover the sporangia. In other 

 cases the indusium is a sac-like cov- 

 ering, which splits (Fig. 311). 



319. The sporangium or spore- 

 case of a fern is a more or less 



iii in i ii ! 305. Fruiting frond of t'lmsi 



globular body and usually with a ,.,.,,, Sori at a ,. 

 Stalk (Fig. 307). 77 contains tin wnw^tth its indusium. at 6. 



spores. When ripe it bursts and the spores are set 

 free. Lay a mature fruiting frond <>t' any fern on white 

 paper, top side up. and allow it to remain in a <ln . warm 

 place. The spores will discharge <>n the paper. 



320. In a moist, warm place (In sports germinate. 

 They produce a small, Hat. thin, green, more or less 



heart -shaped membrane I Pig. 

 312). This is the prothallus. 

 Sometimes the prothallus is 



an inch or more 



across, but oft- 



iiii'i' it is less 

 t han one-fourl h 

 this size. It is 

 commonly an 

 known except 

 t ii botanists. 

 Prothalli maj <>i'ini !" Found in greenhouses where ferns 

 an- grown. Lock on tie- moisl Btone "l- brick walls, or 



I 



I ..nun. .ii polj P0d( 



Polj podium \ "I;;. u . 



;;ii? Sori and poi u 

 gluni "i i"'i> podc. 



