CHAPTER XIII 

 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. 



153. 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 

 structures soon to be described, make it easy to dis- 

 tinguish at once the surface that bears them from the 

 opposite surface. Since the surface bearing the rhizoids 

 lies normally next to the substratum it was called the 

 dentral surface, while the opposite surface was called 

 vorsal. 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 



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