902 



THE NATURE BOOK 



AN ACACIA \('ITH SWELLINGS AT THE BASE OF THE 

 THORNS, \(^HICH ARE INHABITED BY ANTS. 



terference with 

 great fury, 

 rushing out to 

 deal with the 

 aggressor with 

 jaws and stings. 

 The services 

 rendered to the 

 Acacia go even 

 beyond this. 



The South 

 American forest 

 trees are much 



subject to the onslauglits of leaf-cutting 

 ants, whole armies of which ^\■ill. at 

 times, render a district almost denuded of 

 foliage in a short while. The Acacias, 

 which have enlisted the sympathies of the 

 thorn-dwelling ants, are perfectly secure 

 from attack. When the leaf-cutting 

 species arrives on the scene it is to find 

 the situation already occupied b}' hordes 

 of ants fired by the enthusiasm which 

 the defence of a home will always inspire. 

 It is interesting to note the manner in 

 which the ants are encouraged to take up 

 their residence in the thorns. These 

 when young are quite soft, and have their 

 interiors filled with sweet edible pulp. 

 As the insect eats away the contents of 

 that which is to be its home, the thorn 

 swells at the base and thus becomes more 

 commochous. As well, at the bottom of 

 each leaflet there is produced a small 

 sweet gland, and in addition a tiny yellow 

 food body at the end of each division of 

 the leaf. So that it will be seen that the 

 tree makes handsome provision for its 

 army of defenders. It is only during the 

 wet season that such liberal arrangements 

 are made for the welfare of 

 the ants. As soon as the 

 time for the sending out of 

 young shoots is past the 

 honey glands dry up, and, 

 left without their food 

 supply, the majority of the 

 ants perish. A sufficient 

 number, however. sur\'i\e 

 to carry on the race during 

 the time of scarceness. 



Recent in\-estigation has 

 shown that the story of this 

 strange compact between 

 the ant and the Acacia trees 

 is not at all exaggerated. 



LAUREL LEAVHS SHOW 

 ING NECTARIES. 



The same state 

 of affairs has 

 been observed 

 in quite a 

 number of 

 trees. In the 

 case of the hol- 

 lo w-stemmed 

 Cecropias, i t 

 has been found 

 that the speci- 

 mens which had 

 suffered from 

 the attacks of leal-cutting ants were for 

 some reason or other without their body- 

 guard. With the Cecropias the ants 

 enter the stems by means of a little door 

 which they always make at one spot on 

 the stem where the tissue is very thin. 

 Here also the plants are provided with a 

 plenteous supply of food. Near the base 

 of the leaf -stalks are to be found brown 

 patches on which are a collection of oval 

 bodies. These are highly nutritious, and 

 are eaten greedily by the ants. It is 

 certainly significant that, both in the 

 case of the Cecropias and the Acacias, 

 the food bodies are absent where the 

 particular species is not inhabited by 

 ants. 



It must not be supposed that in all 

 cases where ants and other small creatures 

 are found to be associated with plants 

 it is possible to make out a clear case 

 of mutual help. The curious plant 

 Myrmecodia iiiberosa. from the Malay 

 Archipelago, is a case in point. The 

 species is altogether most singular in 

 appearance, and consists of a tuberous 

 growth spreading on the branches of old 

 trees, from the upper part 

 of which spring the fleshy 

 stems bearing the foliage. 

 Every part of the tuber is 

 tenanted by small red ants 

 of a very fierce habit, which 

 rush out and defend their 

 homes when any attack is 

 made. Some years ago, 

 certain observers declared 

 that it was through the 

 agency of the ants that the 

 tuberous growth was formed. 

 Tlie story was seriously 

 placed on record that the 

 bites of the ants caused the 



