THE FORMATION OF HYPHAL FUSIONS 



4i 



connect two successive cells and, as a rule, are not points of departure 



for new lateral branches, the end-cell of each hook, after fusion 



with the third cell from the end of 



the hypha, immediately grows forward 



to form a new very short branch which 



in turn soon becomes hooked at its 



apex. 



From a consideration of the facts 

 just brought forward there seems to 

 be but little doubt that the physio- 

 logical significance of the hook in 

 the Discomycetes is quite different 

 from that of the clamp-connexion in 

 the Hymenomycetes. Whereas the 

 clamp -connexion, as we have seen, 

 may be regarded as a means for 

 facilitating the flow of protoplasm 

 from cell to cell, the hook may be 

 regarded as a means for constructing 

 numerous ascus cells which shall be 

 compactly arranged in a discoid hy- 

 menium. Each ascogcnous hypha 

 bends around at its tip to form a 

 hook, then conjugate nuclear division 

 takes place, after which twin septa 

 are constructed. The result of these 

 operations is that the penultimate cell 

 of the hook is at the top ot the hook 

 and therefore in a good position to 

 develop into an ascus. The terminal 

 cell of the bent hypha, which has 

 become directed backwards and so has 

 taken up a lower position than the 

 ascus cell above it, now fuses with the 

 third cell from the end of the bent 



hypha and immediately thereafter it grows outwards to form a 

 short lateral branch which soon becomes hooked at the end and 



Fiu. 20. — Pyronema confluens. 

 Diagram showing a branched 

 ascogenous hypha forming 

 hooks and asci. The end of 

 the lower branch lias become 

 bent backwards and in it 

 conjugate nuclear division is 

 taking place. In the end of 

 the upper branch conjugate 

 nuclear division has been 

 completed and two septa 

 have been formed ; the ulti- 

 mate cell of the curved 

 hypha, directed backwards, 

 is the hook-cell which is 

 destined to fuse with the 

 adjacent stalk-cell ; while the 

 penultimate cell, which con- 

 tains two nuclei, is destined 

 to develop into an ascus. 

 The uppermost erect cell, 

 containing a fusion nucleus, 

 is a young ascus ; it origin- 

 ated as a penultimate cell 

 in the same maimer as the 

 ] >enultimate cell of the upper 

 lateral branch, and the Jiook- 

 cell below fused with the 

 stalk-cell before it gave rise to 

 the hooked lateral branch 

 which is seen growing away 

 from it. From Mile Ben- 

 saude, after Claussen. 



