1902-1903-] An^s hi Relation to Flowers. 21 



A considerable number of them open early in the morning 

 and remain open until the dew dries up and the troublesome 

 little honey-hunters come forth, when these plants shut up for 

 the day, unless the great business of their life has been got 

 through and they have been fertilised by visitors of the right 

 sort. 



Some few plants are injuriously affected in other ways by 

 the visits of Ants. In a few cases this is due to the action of 

 formic acid upon the plant tissues, which acts in much the 

 same way as most other irritants, by causing an abnormal 

 growth at the spot affected. In some other cases, as in that 

 of the trees visited by the Umbrella Ants of Brazil, CEcodoma 

 ccphalotes, these Ants visit many cultivated trees, such as coffee 

 and orange trees, and cut circular bits out of the leaves, which 

 they carry away over their heads, held like parasols, in order 

 to thatch their wonderful little dwellings. Other leaf-cutting 

 Ants attack the foliage of the Bull's-horn Thorn, a species of 

 acacia found in Nicaragua. But as it is obviously not to the 

 advantage of a tree to be even partially defoliated, some de- 

 fensive means has had to be adopted. In this case, oddly 

 enough, the defensive force enlisted is that of a colony of Ants 

 of a particularly warlike kind, Pseudomyrma hicolor, which are 

 housed by the plant within hollow thorns, and which are pro- 

 vided by the acacia with abundant food and nectar. In 

 return for these services this standing army forms an effective 

 guard against the attacks of the leaf-cutting Ants, as well as 

 against other depredators. My friend Mr Eichard Nicholson 

 of Benalla, near Melbourne, tells me also of the Bull-dog Ant, 

 which in like manner protects the blackberries of Australia 

 from attack. 



There are very many other examples of the same kind, 

 which there is not room to quote here ; but I may conclude 

 this part by some mention of the Serratula described by 

 Kerner, which is liable at a certain early stage of the growth 

 of the flower to the unwelcome visits of a flying beetle, which 

 eats out the tender heart of the flower and ruins it at once. 

 It is not good for the plant that its flowers should meet with 

 a serious injury of this kind, so it has arranged that just before 

 the critical stage in the development of the flower is reached 

 the bracts of the capitulum should each yield a tiny drop 



