442 



REPRODUCTION. 



ences is practically unbroken, reaching from the lowest to the 

 highest forms. The character of this evidence will appear in 

 the succeeding volume of this series. 



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

 back 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 under 

 side of which are pro- 

 duced the sexual or- 

 all of which are 



gans, 



shown in the figures. 

 As a result of the pro- 

 cess of fertilization there 

 is produced a fern-plant, 

 which at its adult age 

 bears the spores above 

 spoken of. 



In any greenhouse 

 where ferns are kept it 

 is easy to procure, by 

 careful search on the 

 soil of the flower-pots, 

 abundance of the pro- 

 thalli in different stages. 

 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 must observe that 

 on the surface of the soil 

 in the flower-pots many 

 other growths are to be 

 found, and care must 

 be taken not to con- 

 found other flat films 

 (belonging, for instance, 

 to Hepaticae) with the 

 prothalli of the ferns. 



Sections through the prothallus will exhibit the sexual organs in different 

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



7? 



A 



213 



FIG. 213. Prothallus of a fern, exhibiting the reproductive organs. At the sinus 

 of the heart-shaped film are to be seen the archegonia, one of which, more highly mag- 

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

 zoids. (Luerssen.) 



