442 



EEPEODUCTION. 



ences is practican3' unbroken, reaching from the lowest to th( 

 highest forms. The character of this evidence will appear in 

 the succeeding volume of this scries. 



(6) True ferns exhibit the following phenomena of fertilization. On the 

 hack of the frond there are formed spores in spore-cases, which are variously- 

 grouped and protected. 

 The spores on reaching 

 a fit surface soon give 

 rise to thin films (pro- 

 thalli), on the nndei 

 side of which are pro- 

 duced the sexual or- 

 gans, all of which are 

 shown in the figures. 

 As a result of the pro- 

 cess of fertilization there 

 is produced afem-plant, 

 which at its adult age 

 bears the spores ahove 

 spoken of. 



In au\' greenhouse 

 where ferns are kept it 

 is easy to procure, hy 

 careful search on the 

 soil of the flower-pots, 

 abundance of the pro- 

 thalli in differentstages. 

 The most minute of 

 these exhibit the sexual 

 organs just forming, 

 while those which are 

 more advanced give all 

 the features shown in 

 the figures. The stu- 

 dent m ust observe that 

 on the surface of the soil 

 in the flower-])Ots many 

 other growths are to he 

 found, and care must 

 be taken not to con- 

 found other flat films 

 (belonging, forin stance, 

 to Hepaticije) with the 

 prothalli of the ferns. 

 Sections through the prothallus will exhibit the sexual organs in diflFerent 

 stages of development. The best material is procured by the cultivation of 



Fig. 213. Protliallus of a fern, exiiibiling tlie reproiluctive organs. At the sinus 

 of tlie heart-shaped film are to be seen the archegoiiia, one of which, more higlily mag- 

 nifleil, is displayed in section in A. B, an enlarged antheridium with escaping anthero- 

 zoids. (Luerssen.) 



