THALLOPHYTA— FUNGI 



67 



many gametophytes are only potential ones, usually producing 

 gonidia alone. Many generations of these may occur in suc- 

 cession before an actual one with sexual organs is formed. 

 Hence we get often, as in the Algse, in the life history an alterna- 

 tion, generally very irregular, of potential with actual gameto- 

 phytes, in addition to the alternation of sporophyte with gameto- 

 phyte, which is also very irregular. The former has been called 

 homologous, the latter antithetic alternation. 



Again, some of the gametophytes have lost the power of 



Fig. 817. 



Fig. 817. CcEnocyteof J/ucor J/ucerfo, bearing a sporangium or gonidangium, 

 k. This is more bighly magnified in tlie fig. to the right, m. Columella. 

 I. Gonidia or spores. 



producing sexual cells at all, probably in consequence of the 

 degeneration of structure that has accompanied the parasitic or 

 saphrophytic modes of nutrition. They thus never produce any 

 reproductive cells but gonidia, and can only be distinguished as 

 gametophytes by a careful study of their homologies. 



Polymorphy is very wide-spread among the Fungi. As we 

 have seen, the plant body is in most cases the gametophyte. It 

 may be unicellular, consisting of separate cells of various shapes, 

 rounded, oval, or irregular. It may be a coenocyte (fig. 817), 

 when the appearance it presents is that of a number of white 



f2 



