190 COMPARATIVE MORPHOLOGY OF FUNGI 



Like the imperfect forms, the sexual organs are directly connected to 

 the Endomycetales and Zygomycetes, only the dynamic differentiation 

 between the male and female copulation branches becomes morphologi- 

 cal and, in the majority of forms, has led to special antheridia and asco- 

 gonia which are characteristic both in form and function. As the 

 imperfect form, so the sexual organs show development in three direc- 

 tions. A first direction (Monascus-Magnusia) is distinguished by the 

 functional development of the female copulation branch. This no longer 

 participates as a whole in fertilization but is differentiated into a 

 trichogyne and a female gametangium, the ascogonium. Herein lies the 

 root of the relationships in many higher Ascomycetes. 



A second series (Gymnoascus-Aspergillus-Penicillium group) develops 

 in the reverse direction, with the gradual disappearance of sexuality. 

 Already in the simpler forms the sexual act has become facultative. In 

 the higher forms, the formation of the antheridium is more and more 

 delayed and can only function when the ascogonium has already passed 

 the stage of maturity for fertilization and has become multinucleate or is 

 already septate. Hence the ascogonia probably develop parthenoge- 

 netically. When the antheridia are still formed, perhaps they only fulfil 

 a physiological function of nourishment, and hence are called "tropho- 

 gones" by Dangeard (1907). They are soon no longer formed and the 

 ascogonia develop alone. 



In the third series (Penicilliopsis-Elaphomycetaceae) the sexual organs 

 no longer initiate the formation of fructifications but function within 

 them. 



While the imperfect forms and sexual organs of the Plectascales corre- 

 spond with the Endomycetales and Zygomycetes in the further develop- 

 ment of the zygotes, there appears a new factor, the dicaryophase and 

 the development of the ascogonial cells to ascogenous hyphae. Thereby 

 the developmental scheme of the Plectascales is lengthened by one mem- 

 ber from that of the Endomycetales (p. 146) : 



I 

 jt Secondary spore forms 



11 ^^ P C R 



Mycelium— ^Sexual organs— ^Ascogenous hyphae— >Asci— *Ascospores 



Diagram XIX. 



In several forms the ascogenous hyphae show a peculiar separation 

 into two phases; thus in Aphanoascus they first grow spirally ("primary" 

 ascogenous hyphae), the branches again coil ("secondary" ascogenous 

 hyphae); only the second generation forms the asci. More sharply 

 distinct is the division in Penicillium "crustaceam;" where the ascogenous 

 hyphae are developed into a resting and a spore-forming period. At 

 present no interpretation of this change of ascogenous hyphae is evident; 

 we meet it, however, in the Erysiphaceae. 



