GENERAL SUMMARY 373 



the word peg is meant a very short special fusion hypha which has never 

 grown freely in the medium by itself but has been stimulated to come 

 into existence by another hypha, another peg, or a hook with which it 

 is destined to fuse ; and by the word hook is meant a very short curved 

 hypha such as is always produced during the formation of a clamp- 

 connexion. A peg may be regarded as a fusion organ. 



In the formation of a clamp-connexion (hook-to-peg fusion) the stages 

 of development follow a definite sequence as follows : (1) a hook grows 

 outwards, backwards, and inwards towards the main hypha, (2) conjugate 

 nuclear division takes place, (3) a septum is formed across the main hypha 

 at the level of the middle of the hook, (4) a septum is formed across the 

 top of the hook, (5) the main hypha sends out a peg opposite the end of 

 the hook, (6) the end of the hook and the end of the peg flatten out 

 against one another, (7) the double wall between the hook and the peg 

 is dissolved away, and (8) the nucleus that was imprisoned temporarily 

 in the hook-cell escapes from the hook into the main body of the penulti- 

 mate cell of the hypha. In Coprinus lagopus this sequence of events, 

 under favourable conditions of growth, may be accomplished in 23 minutes. 

 The conjugate nuclear division takes place in less than 14 minutes and 

 probably in about 12 minutes. 



In Hymenomycetes and Gastromycetes, in both haploid and diploid 

 mycelia, each septum has a small central open pore through which 

 protoplasm can pass from cell to cell. 



In Hymenomycetes and Gastromycetes, under natural conditions, the 

 haplophase of a mycelium very soon passes into the diplophase and, as 

 a rule, fruit-bodies are formed not on haploid but on diploid mycelia. 



In Hymenomycetes and Gastromycetes the clamp-connexion may be 

 regarded as a means for providing between any two adjacent cells of 

 a diploid mycelium two septa instead of one and therefore two passage- 

 ways for protoplasm instead of one. Thus, owing to the existence of 

 clamp-connexions, the translocation of the protoplasm of a diploid 

 mycelium into a fruit-body, when this is being formed, is facilitated. 



The hooks of the ascogenous hyphae of Pyronema confluens and other 

 similar Discomycetes are regarded by the author as differing from the 

 clamp-connexions of the Hymenomycetes in (1) their physiological 

 significance, (2) their mode of development, and (3) their evolutionary 

 origin. 



Throughout the Hymenomycetes and Gastromycetes, the hook of 

 a clamp-connexion grows backwards and not forwards. If the hook of 

 a clamp-connexion were to grow forwards instead of backwards, the 

 terminal cell of each hypha, in which alone growth in length takes place, 

 would periodically (during the formation of each clamp-connexion when 

 a nucleus is temporarily a prisoner in the hook-cell) have its nucleo- 

 plasm^ ratio upset to the extent of being reduced to one-half, thus 

 affecting growth adversely ; whereas, when the hook grows backwards, 



