25 4 PETCH : THE FUNGI 



(17) regards them as galls. andSchimper (19) states that they 

 represent a new structure which has arisen as a result of 

 artificial selection exercised by the ants. Moller himself says 

 ' Die Kohlrabikopfe sind neue, morphologisch bestimmte 

 Gebilde geworden. welche ihrer Fadennatur bereits so weit 

 entfremdetsind, dass sie nur in seltenen Fallen noch nachtrag- 

 lich zu Faden auszuwachsen vermogen," and he traces in the 

 species of ants investigated by him a gradually increased 

 specialization of these structures. In the lowest form (nest 

 of Cyphomyrmex aur it 'us . Mayr. fig. 38) the swellings occur irre- 

 gularly in the course of the hyphae; they vary in size, and all 

 stages from normal hyphae to strongly swollen ones are found 

 entangled together. A higher development is seen in the nest 

 of Cyphomyrmex strigatus, where the size of the swellings is 

 more regular though their shape and position is still variable. 

 In Apterostiyma Wasmanni they are cylindrical, but occur at 

 the tips of the hyphae. Finally, in the genus Atta (Acromyrmex) . 

 the swollen hyphae ends are spherical and are grouped in more 

 determinate heads than in the other three cases (fig. 37). 



As long as the only recognized type of agaric mycelium 

 consisted of a system of filamentous hyphae sometimes united 

 into strands, it was reasonable to regard the spheres of the 

 ant nests as special structures evolved by cultivation in a 

 mycelium which exhibited a strong tendency to produce irre- 

 gular swellings on the hyphae. Schimper states : " These peculiar 

 structures are a product of cultivation comparable with 

 Kohlrabi. The phylogenetic starting point of their evolution 

 is to be found in the tendency of the fungus to produce all kinds 

 of swellings." 



But the re-discovi y of the fact that a normal mycelium may 

 consist of a mass of small spheres built up of swollen cells 

 affords another explanation. It seems most probable that 

 Moller"s " Kohlrabihiiuf chen " are part of the normal mycelium 

 of an agaric, and that their form is due to cultivation by the 

 mis only in a small degree, if at all. The stages of develop- 

 ment in the nests of different species may then be attributed 



