DEFENCE. 97 



is probably a very rare phenomenon with plants in 

 a state of Nature, 



The defensive armour of plants is generally adapted 

 to resist many different evils. The more important 

 general protections are the following : 



(i) Cork and the other outside or "skin" pro- 

 tections. 



(2) Latex, or milky juice containing indiarubber or 

 caoutchouc. 



(3) Resins, such as Turpentine, etc. 



(4) Tannins. 



(5) Acids, Alkaloids and other bodies with strong 

 medicinal properties, including vegetable poisons. 



(6) Scents. — Strong-smelling ethereal oils, such as 

 Lavender and Mint. 



(7) Crystals. 



The more special defensive weapons are : 



(8) Thorns, Spines, and Prickles. 



(9) Stinging Hairs. 



(10) Ants of a fierce disposition which keep off 

 leaf-cutting insects. 



Outside Protections. — That part of the plant, 

 which is on the outside, is always covered by a special 

 skin, which is intended to guard against fungus and insect 

 enemies, and which also prevents the evaporation of the 

 water or sap which fills the tissues. Vegetable cells 

 always contain a very large proportion of water when 

 alive, and they are dependent upon it for their 

 nourishment ; hence it is very necessary that the 

 water should not escape unless it is intended that it 

 should do so. (See p. 100.) The character of the skin 

 varies ; young parts are generally covered by the 

 original epidermis. The older branches and trunks of 

 the Pines and Dicotyledons are almost always covered 



(B7) G 



