136 TYPE STUDIES 



are cut off from the sides of the apical cell to form the root and from 

 its base to form the root cap. Trace the history of these segments in 

 your preparation. Draw. 



F. The (jermmation of the sjwres. Examine a two- or three- 

 weeks-old culture of fern spores sown on earth or on old, 

 dirty flowerpots (Sec. 208). Spores are to be found in vari- 

 ous stages of germination. The structure developed from 

 the spore is called a prothalUum. It will, however, become 

 apparent from the study of a mature prothallium that the 

 structure is a gametophyte. Note : 



1. The ruptured spore and protruding green filament. 



2. The change of the tip of the filament into a flat plate of 

 cells by the formation of oblique walls, which cut out a 

 wedged-shaped apical cell. 



3. The development of rh Izoids. Where ? 



4. As development proceeds the apical cell becomes situated 

 in a notch on account of the growth of the cells on both 

 sides, and the prothallium takes a heart-shaped form. 



Draw a series of stages in the germination of the spores 

 and development of the prothallia. 



G. The mature prothallia, or gametophytes. Examine a large, 

 heart-shaped prothallium six or more weeks old. Observe its 

 thalloid structure, the angle at which it rises from the sub- 

 stratum, the position of the notch. Mount with the lower 

 side uppermost. Note : 



1. The position of the rhizoids. 



2. Small, round antheridia, many of them probably open 

 and brownish, situated at the lower or posterior end of 

 the prothallium. 



3. The projecting necks of archegonia just back of the notch 

 on a thicker region of the prothallium called the cushion. 



Show the position of these structures in an outline sketch. 

 The prothallia are gametophytes, since they produce sexual 

 organs, arise from the asexual spores of the sporophytes (fern 

 plants), and alternate with this asexual generation. 



