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 
wrsaL 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, b\it 
the application of the terms would not be changed if 
the differentiated prothallus should happen, by any 
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