2 COMPARATIVE MORPHOLOGY OF FUNGI 



appropriate letters above. The haploid phase is underlined by a narrow 

 line, the diploid by a broad one. 



The extent of development of haplont and diplont are very different 

 for different groups of organisms. On one extreme the thallus (vegeta- 

 tive body) is haploid and the diplont is reduced to a zygote incapable of 

 separate existence. There are many intermediate cases to the other 

 extreme in which the thallus is diploid and the haplont is reduced to a 

 few cells parasitic on the diplont. An intermediate condition is reached 

 in forms in which haplont and diplont are two distinct thalli. Haplont 

 and diplont here follow each other as two morphologically different 

 generations. In this case we have alternation of generations. The 

 haploid generation is called the gametophyte, the diploid, the sporophyte. 

 These relations are further complicated in certain cases where an organ- 

 ism regularly passes through several different, morphologically distinct 

 stages of development within the same nuclear phase, e.g., the protonema 

 and moss plant in the haploid phase of mosses and the larval, pupal and 

 imago in the diploid phase of insects (Maire, 1900, 1902; Lotsy, 1907; 

 Buder, 1916; Goeldi and E. Fischer, 1917; Kylin, 1917; E. Fischer, 1919; 

 Svedelius, 1921, 1927). 



These different rhythms are not so strongly fixed in the fungi as in 

 higher organisms. They have been modified and have displaced one 

 another because of parthenogenesis, apogamy, apomeiosis, because of 

 environmental changes or because of retardation or hindrance of fertili- 

 zation or of meiosis. Since the comparison of these rhythms makes a 

 desirable scheme in which to arrange morphological facts, it will be 

 given the chief emphasis in this book. It is the aim of comparative 

 morphology to follow the cytological development of the life cycle and 

 to examine the ontogeny of thalli and fructifications by comparing them 

 in both phases. 



