130 



COMPARATIVE MORPHOLOGY OF FUNGI 



rather far separated; shortly the process bends around into a hook (Fig. 

 79, 2) and the nuclei begin to divide conjugately and to draw into a layer 

 (Fig. 79, 3). The spindles lie approximately parallel to each other. 

 After the division, the crook is abjointed from both the tip and the stipe 

 (Fig. 79, 4) ; thus the crook contains two nuclei, while the tip and stipe 

 contain one nucleus each. In the simplest case, the nuclei of the crook 

 fuse to a diploid nucleus, the primary ascus nucleus (Fig. 79, 5), and the 

 crook develops to an ascus. In another case, the crook develops to a 

 new hook, which again develops, etc., so that several lie transitorially 

 behind one another (Fig. 79, 6 to 8) ; only the last terminal hooks proceed 

 to ascus formation. In the third case, the dicaryon of the hook divides 

 without a previous formation of a new hook. The crook develops a 

 branch which only later returns to hook formation; on these hooks, asci 

 may arise directly; or caryogamy may be again displaced, so that a tuft 

 of hooks arises (Fig. 79, 8). By the combination of these various possi- 



Fig. 80. — Geopyxis catinus. 



Development of ascogenous hyphae. 

 1905.) 



(After Guillermond, 



bilities there have arisen those manifold pictures which have so long 

 delayed the morphological comprehension of ascogenous hyphae. Occa- 

 sionally hook stipe and hook tip fuse, the stipe nucleus generally migrat- 

 ing into the tip (Fig. 79, 5 and 6); the tip cell which has now become 

 binucleate develops a branch which gradually forms a hook; this hook 

 can, by fusion of its nuclei, develop directly to an ascus or again (Fig. 79, 

 8) grow into a transitory tuft of hooks. 



Besides the characteristic formation of hooks, the ascogenous hyphae 

 of Pyronema confluens pass through two morphologically different phases 

 of development. In the first phase (directly after development from 

 ascogonia), they are coenocytic and longitudinally striate and develop 

 with normal growth of the tip; in the second phase (after the growth from 

 septate hyphae), they only develop further by hook formation and have 

 only one dicaryon in each cell. The most striking development of pri- 

 mary and secondary ascogenous hyphae, we meet in the Plectascales. 



In addition to the hook type, a whole series of other developmental 

 forms of ascogenous hyphae is known in the higher Ascomycetes. In 



