1 89C.] MICROSCOPICAL JOURNAL 77 



liaps tlic greatest scourge to vegetation, and an army of 

 these will destroy in a single night the entire foliage of 

 a tree. Now any such attack upon a trumpet-tree rouses, 

 not only the anger of the honey-eating ants which are 

 being fed at its expense, but calls forth their instinct of 

 self-preservation, for upon the welfare of their host plant 

 depends their own life. Hence they constitute them- 

 selves a defending force, and in the fight between the 

 t,wo armies of ants which ensues, they are generally vic- 

 torious, perhaps because they are fighting for house and 

 home, while the intruders have only come for plunder. 



The mutual advantage then is clearly established by 

 the observation of these spirited encounters, and we have 

 here an explanation for many of those nectaries which 

 are found, not inside the flowers, but on leaves and leaf- 

 stalks, and have hence been termed extra-floral nectaries. 



But the trumpet-tree is not the only tree supplied 

 with ants; many acacias allow ants to make their home 

 in their hollow spines, which are found at the base of the 

 leaf, and are indeed the transformed stipules of those 

 leaves. Myrmecodia again has the lower portion of its 

 stem curiously swollen up, and in this dilated portion run 

 large and intricate galleries, which are peopled with 

 ants, enticed into these chambers and fed by the plant. 



Then we have curious instances in which, for a time at 

 least, plants will give protection and food to an animal 

 for some benefit derived from it, not in the form of pro- 

 tection from attacks, but usually by securing the fertili- 

 sation of its ovules. Fertilisation of plants by the agency 

 of insects takes place to a large extent; the pollen of one 

 flower is carried by insects, such as bees and moths, to 

 the stigma of another flower, which is then said to be 

 pollinated, and further changes in the pollen-grain lead 

 to the fertilisation of the ovules contained within the 

 ovary. It is for the purpose of attracting these insect- 



