INSECTS AND FUNGI 235 



must be always present in the comb. The termites must 

 " weed out " all foreign fungi, and Xylaria nigripes is the one 

 species which defies their efforts to exterminate it. 



The Fungi of Leaf-cutting Ants 



The leaf-cutting ants investigated by Moller cut small discs 

 from living leaves and carry them into their nests ; there they 

 bite them into small fragments and knead them into balls. 

 These balls form the foundation of the fungus garden, and 

 are fastened together by the hyphae of the fungus. It is at once 

 evident that there can be no sterilisation of this material, and 

 that fungi of all kinds must be taken in with it. The cultivated 

 fungus is more abundant than that in a termite comb, but 

 it resembles the latter in bearing small white tufts, which are 

 eaten by the ants. But the structure of these tufts shows 

 nothing of the complexity of the termite spheres. Each tuft 

 consists of hyphae with swollen ends, mixed with other normal 

 hyphae, and there is no definite arrangement. They show the 

 simplest variation it is possible to get in a fungus hypha. 

 Moller calls these swollen hypha ends " kohlrabi heads." 



At rare intervals, an agaric grows in clusters on the top 

 of the fungus garden. The latter is near the surface or is 

 merely covered with dead leaves, and there is therefore no 

 elongation of the stalk or modification of the agaric such as 

 occurs in the termite nest. Moller was able to germinate the 

 spores of this agaric, and to grow from them a mycelium which 

 developed kohlrabi heads, though it may be objected that 

 recurrence of such a simple modification does not necessarily 

 denote identity. 



So far the parallel is complete, although all the fungi of the 

 termites are more complex than those of the leaf-cutting ants. 

 A difference apparently arises in the growth of the fungus 

 garden after the ants have been removed, and in the cultures 

 made with the mycelium of the garden. When the fungus 

 garden is enclosed in a glass dish, the kohlrabi tufts collapse, 

 just as the termite spheres do under the same conditions. 

 After a few days a dense growth of hyphae covers the garden 

 and soon develops conidia ; and in a few days more, hyphae of 

 a different kind appear and develop conidia which differ from 

 the first. Moller regards these two " moulds " as conidial 

 fructifications of the agaric ; but the evidence hardly seems to 



