THE FUNGI : ASCOMYCETES AND BASIDIOMYCETES 321 



This only occurs when hyphae of ( + ) and ( - ) strains come into contact. A 

 clamp connection is then formed (Fig. 314). In this process a small hook- 

 like outgrowth is formed from the side of the cell. We will call the nucleus 

 nearest to the hook A and that 

 farthest off B. Nucleus A enters 

 the hook, and both A and B divide 

 simultaneously. The two daughter 

 nuclei of B separate widely, one lying 

 on each side of the place where the 

 hook has formed. One daughter 

 nucleus of A moves back into the 

 cell and then two contiguous cross 

 walls are formed, one cutting off the 

 hook from the cell, the other cutting 

 the parent cell in half. Lastly, the 

 tip of the hook fuses to the hypha 

 and the other daughter nucleus of 

 A moves into the cell to join the 

 daughter nucleus of B. The result 

 is two cells, each containing one 



daughter nucleus from both A and Fig. 313.— PW//o?rt campestris 

 B. The hook remains as a per- 

 manent attachment of the hypha. 

 Every subsequent division is carried out in the same way. The possession 

 of clamp-connections is therefore a mark of a binucleate mycelium. 



Mature fruiting 

 body taken to show the annulus and the gills 

 bearing dark spores. 



r\ 







r\ 



r\ 



B 



r\ 



fr 











f 







D 







Fig. 314. — Diagram of clamp connections. A to E, Successive stages in the 



process. For details see text. 



The mycelium remains binucleate until fruiting bodies or sporophores 

 are formed, which, so far as is known, can only develop on a mvcelium of 

 this type. During the development of the fruiting body some of the cells 

 become multinucleate, though the basidia are binucleate. 



