CHAPTER II 

 LIFE HISTORY OF A FERN (Concluded) 



The prothallus, as just described, bears little resem- 

 blance, indeed, to the fern plant with which we are com- 

 monly familiar. In fact , the relation between the two was 

 not understood, nor even suspected, until about 1848, 

 when Count Lesczyc-Suminski, a Polish botanist, first 

 gave a connected description of the life history of the fern. 

 We shall now proceed to follow the steps which lead from 

 the prothallus to the new sporophyte. 



13. Dorso-ventral Differentiation. — ^The appearance of 

 the first root-like body, or rhizoid, was noted above. 

 As the prothallus develops the rhizoids become more and 

 more numerous, forming a mass of fine thread-like bodies 

 on the under side, opposite the notch, of the heart-shaped 

 prothallus. The presence of rhizoids, and of other struc- 

 tures soon to be described, makes it easy to distinguish 

 at once the surface that bears them from the opposite 

 surface. Since the surface bearing the rhizoids lies nor- 

 mally next to the substratum it was called the ventral 

 surface, while the opposite surface was called dorsal. As 

 now used, the terms dorsal and ventral are morphological 

 terms, and have no reference to the manner in which the 

 prothallus lies. Normally the ventral surface is the under 

 one and the dorsal surface the upper, but the application 

 of the terms would not be changed if the differentiated 

 prothallus should happen, by any chance, to lie upside 



