SOME KEMARKABLE ADAPTATIONS OF PLANTS TO INSECTS. 99 



Ants as Cultivators of Fungi. 



Dr. Schimper observes : * — " Ants in the temperate zones play an 

 unimportant part in the economy of nature, but in the tropics a leading 

 part. In tropical America the so-called leaf-cutters, or parasol-ants, of 

 the genus Atta, may be reckoned as the most dangerous foes to vegeta- 

 tion." 



The object of the ants in cutting fragments of leaves, flowers, fruits, 

 or seeds, which they carry home, often from great distances, is to form 

 beds for the cultivation of fungi. " The fragments are cut up at home 

 into small pieces and kneaded soft by the feet and mandibles, so that but 

 few cells remain unbruised." This spongy mass forms the fungus-garden. 

 Fine mycelial threads soon interpenetrate the mass of decaying vegetable 

 matter. The branches of the mycelium bear innumerable white bodies, not 

 more than ^ inch in diameter. " They spring laterally from the mycelial 

 threads, and are termed by Moller ' kohl-rabi clumps.' " They consist of an 

 agglomeration of short, branches with globular swollen ends and very rich 

 in protoplasmic contents. They are the most important, if not the sole 

 food of the ants, and represent a new structure which has arisen. Moller, 

 of Brazil, noticed how " the ants by industriously biting off the sub- 

 aerial threads prevent the vegetable sprouting and the formation of large 

 pileate sporophores of a purely agaric type, which Moller found to be a 

 new species, which he named Bozites go7igylophora." This may possibly 

 explain the origin of the " clumps " ; for M. Gallaud in his investigations 

 upon endophytic Mycorrhiza noticed that as the mycelium penetrates 

 through the cell-walls of the host the check received often causes the 

 branchlet to swell into a " vesicle," apparently very like those of the 

 kohl-rabi clumps. 



Dr. Schimper adds : — " The four species of Atta that occur near 

 Blumenau cultivate the same species of fungus, which is never found 

 outside the ants' nests. We have therefore here a highly developed case 

 of reciprocal adaptation between unlike organisms." 



It must be added that, although the clumps only arise in nature 

 under the treatment of the ants, Moller was able, in cultures in nutritive 

 solutions, to induce the fungus to form kohl-rabi clumps, which were 

 identical with those in the fungus-gardens, and were eaten just as greedily 

 by the ants. " The phylogenetic starting-point of this evolution is to 

 be sought in the tendency of the fungus to produce all kinds of swellings." 



There are other genera of ants which also make fungus-gardens : one 

 is called the hump- backed ant. The mycelium develops less perfectly 

 formed kohl-rabi clumps, having only swollen club like forms of branches. 



Floral Adaptations to Insect Pollination, 



The adaptations of flowers may be regarded as the result of a response 

 of the living protoplasm together with its nucleus, due to its inherent 

 sensitiveness to external irritations, or what Darwin called " the direct 

 action of the conditions of life." 



But there is more than a mere response. The structures show in 

 many ways remarkable "means to ends," as we should describe them 



* Op. cit. p. 134. 



