I lO PLANT LIFE. 



Stinging Hairs such as we find in the Nettle and its 

 allies are also important weapons of defence. The nettle 

 has a partiality for waste places near human dwellings, 

 and it would soon be trodden down were it not for its 

 stinging hairs, and its habit of growing in dense clumps 

 which are made up of many stems springing from an 

 underground, much-branched root-stock, often eight feet 

 or more in length. The leaves are quite wholesome, for 

 they can be made into either tea or spinach; and they 

 are especially good for poultry. String also can be 

 made from the bark, a yellow dye from the roots, and 

 oil can be obtained from the seeds. Yet the stinging 

 hairs seem to protect it from everything except cater- 

 pillars and fungi. Some foreign nettles have much more 

 poisonous stings. The Devil's Leaf ( Urtica urentissimd) 

 stings so severely that its effects may be felt for twelve 

 months ; and the sting of a handsome Australian tree, 

 Laportea moroides, may even kill horses. 



Myrmecophily. — The last and most interesting 

 method of defence consists in the plant using some kind 

 of insect as a species of police, or army, to keep off injuri- 

 ous insects or larger animals. These defenders are chiefly 

 found in tropical countries where leaf-cutting ants which 

 live in colonies and strip whole trees to form their nests 

 are not unusual. The best known case is that of some 

 South American Acacias. The plant has hollow thorns 

 and upon the tips of its leaflets there are small projec- 

 tions which are full of sugary material. The hollow 

 spines are inhabited by colonies of fierce soldier ants, 

 which swarm out, and drive off any insect enemy, 

 and are fed, or " boarded," on the food-bodies of 

 the leaflets. In this country there are no leaf-rutters, 

 and few soldier-ants, so that similar arrangements are 

 not employed. Nevertheless honey is secreted by the 



