112 COMPARATIVE MORPHOLOGY OF FUNGI 



intertwine with the neighboring hyphae into a solid felt whose outer sur- 

 face is cuticularized and brown. Within this tissue lies the zygospore. 

 Thus in Mortierella, for the first time in Phycomycetes, a true fructifica- 

 tion is formed, in Brefeld's terminology, a carpospore. 



The zygospores germinate only after a long resting period. The 

 exospore is ruptured, the endospore puts forth a germ tube which develops 

 to a mycelium or, with insufficient nourishment, directly to a sporangium 

 (Tig. 66, 5) or a conidiophore. 



During germination, meiosis of the diploid nuclei occurs. Where the 

 germ tube becomes the fundament of a sporangium (e.g., Phycomyces 

 nitens; Burgeff, 1915) meiosis only occurs in the latter which is called a 

 germ sporangium and, as we shall see later, is the precursor of the ascus. 

 The sexual relationships existing at meiosis have been more closely 

 studied for three type (Sporodinia, Mucor Mucedo and Phycomyces nitens; 

 Blakeslee, 1904, 1906). In Sporodinia the sporangiospores are homo- 

 thallic and the separation of the + and — energids occurs only in the 

 formation of the copulation branches. This life cycle may be represented 

 in the following scheme which corresponds in its fundamental characters 

 to that of Polyphagus and Saprolegnia: 



f ± Sporangia — *■ ± Sporangiospores 



P C R 



+Spore— *± Mycelium^+Gametangia— *-(-Coenogamete Coeno— >Zygo— *± Mycelium 



v zygote spore 



— Gametangia— >— Coenogamete 



Diagram IX. 



In the heterothallic Mucor Mucedo, the separation of the + and — 

 energids occurs probably in the formation of sporangia; i.e., the spores 

 are all of one sex in one sporangium and are all + or all — : 



+ Sporangium 



| y -(-sporangium — >■-(- p C R t 



+ Mycelium ^+G^metangium-*+Coenogamete I Zvgo8pore _ ± Mycelium 

 vcelium— >■— Gametangium— »— Coenogamete )•'=>*' i 



L- ^-Sporangium-*- -Sporangium 



Diagram X. 



In the equally heterothallic Phycomyces nitens, the separation of sexes 

 occurs only in the formation of spores. Even so, it is incomplete: besides 

 the + and — spores, there are also unstable, neutral, bisexual spores in 



