FERNS 



193 



slide, and under a low power watching them as they dry 

 and burst. 



110. Gametophytes. In continuing the life-history of a 

 fern, the spores when discharged, as just described, begin 

 to germinate, provided they have reached suitable con- 

 ditions. Each germinating spore produces a green thallose 

 body that resembles a very small delicate liverwort 

 (Fig. 186). It is deeply notched, having a general heart- 

 shaped outline, and 

 is usually less 

 than one-fifth of 

 an inch in diame- 

 ter. This thallus 

 is so thin that all 

 its cells contain 



chloroplasts, and ^Il)fMW\ ,,/. Ill 



rhizoids from the 

 under surface an- 

 chor it to the soil. 

 It is evident that 

 it is an indepen- 

 dent plant, al- 

 though a very 

 small one. Upon 

 this minute plant 

 the sex-organs are 



produced, and therefore it is the gametophyte in the life- 

 history. This fern gametophyte, because it is a thallus 

 body which precedes the appearance of the large sporo- 

 phyte, has been called the prothallium (or prothallus), 

 and this name has come to be very commonly used for 

 gametophyte among all the higher plants. At the bottom 

 of the conspicuous notch of the prothallium is the grow- 

 ing point, representing the apex of the. plant. 



The antheridia and the archegonia are produced on the 



FIG. 186. Gametophyte (prothallium) of a fern: A, 

 under surface showing rhizoids (rh), antheridia (an), 

 and archegonia (ar); B, under surface of an older 

 gametophyte, showing the young sporophyte, with 

 root (w) and leaf (f>). After SCHENCK. 



