DEFENCES OF PLANTS 347 



animals may be repeated with similar results. After 

 repeated primings the tree has the appearance of a 

 garden tree that has been pruned into some conven- 

 tional shape. But after some years of pruning, the 

 time comes when animals leave the tree alone. The 

 tips of the mutilated shoots which become dry and 

 hard are eventually so crowded, and the branches be- 

 come so thick and sturdy, that a grazing animal attempt- 

 ing to reach young leaves pushes its nose against hard 

 points that hurt in a tender spot. This is a suggestive 

 issue. The aggressor against a defenceless tree un- 

 consciously causes the eventual appearance of a de- 

 fensive armour, which renders the tree immune to 

 further attack. Beech hedges that are regularly pruned 

 develop armour of the same description. 



Many plants find safe refuge under hedges and trees 

 which keep grazing animals at bay by means of their 

 protective armour. On a hedge-bank such plants as 

 the Stitchworts, Wild Vetches, Vetchlings (Lathyrus) 

 Ground Ivy, Wild Parsley, Sweet Cicely, White Dead- 

 nettle, and Chervil, grow with great success and un- 

 molested in spite of the fact that a number of them 

 make excellent fodder. The Sweet Cicely (MynMs 

 odorata, Plate XVIII.) is one of the Umbellif erse ; it pro- 

 duces fruits with a pungent aromatic flavour, which 

 probably serves to prevent birds from attacking them. 

 The White Deadnettle (Lamium album) is frequently 

 seen in association with Stinging Nettles, and when "this 

 is so, its warlike neighbour may keep grazing animals at 

 a distance. It also happens that this plant has leaves 

 which in general appearance closely resemble those of 

 the Stinging Nettles. Perhaps animals are deceived by 



