CHAPTER IV 

 SEXUAL ORGANS AND SEXUALITY 



The sexual function involves two processes: (a) fertilization, i.e., 

 a fusion of two nuclei, periodically recurring in the course of development 

 and setting free specific stimuli for development; and (b) meiosis, i.e., a 

 return to the single chromosome number. This rotation (haplont- 

 fertilization-diplont-meiosis) forms the changes of nuclear condition 

 mentioned in the introduction. A few fungi seem to exist without a 

 change of nuclear condition; they seem to be accustomed to living an 

 unlimited number of "generations" without reconstruction of their 

 nuclei and to propagate themselves by imperfect stages only. These 

 fungi with incomplete, or incompletely known, life cycles are called 

 Fungi Imperfecti or Deuteromycetes. 



The fungi with complete life cycles are divided, as are all other sexual 

 organisms, into monoecious (bisexual or hermaphroditic) and dioecious 

 forms. In contrast to the higher plants, in these fungi the question of 

 the division of sexes is limited to the haplonts, i.e., the thallus, and the 

 monoecious forms are called homothallic or neutral and the dioecious 

 forms, heterothallic. The former are indicated as ± , the latter as + or 

 — . The + and — mycelia of the latter group may be distinguished 

 from each other only dynamically (i.e., only physiologically, as a result 

 of their sexual tendencies) or morphologically (e.g., in growth form, 

 sexual dimorphism). 



The process of fertilization in fungi, as in algae and protozoa, may be 

 demonstrated in many ways (Winkler, 1908; Hartmann, 1909, 1918; 

 Guillermond, 1913; Ernst, 1918). The simplest normal type of fertili- 

 zation, when two spatially separated, not closely related sexual cells 

 fuse to form a new entity, is called amphimixis. 



If these sexual cells arise as daughter cells of a characteristic mother 

 cell and are themselves characteristically formed, they are called gametes 

 and the mother cells gametangia (Fig. 11, 13 to 15). The copulation of 

 two specific gametes of this type is called merogamy. If the gametes are 

 equivalent to each other, the copulation is called isogamous, if the gametes 

 are different, their copulation is heterogamous. If in the latter case one 

 gamete is motile, the other non-motile, the former is called sperm (sper- 

 matozoid) and the latter, egg (Fig. 34). In the lower fungi, the gametes 

 are doubtlessly derived from zoospores which are weakened by under- 



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