102 ETON NATURE-STUDY 



the prickles are, but a closer examination will reveal the secret. 

 Again, let him find an answer to the question, " Why are desert 

 plants so often prickly ? " 



MEANS OF DEFENCE OF ROOTS 



No doubt there are a great many plants that have not found it 

 necessary to protect their roots in any special way, being successful 

 enough in the struggle for existence without having to do so. 



On the other hand, however, there are some exceptions, the soap- 

 wort for instance, the roots of which never seem to suffer from 

 attack. They produce a bitter nauseous substance which renders them 

 distasteful to most, if not all animals. The monk's-hood, again, has a 

 highly poisonous root. Here perhaps for once the student will have 

 to rely on book knowledge and hearsay, as actual experiment in this 

 line would be difficult, not to say dangerous. 



How PLANTS HEAL THEIR WOUNDS 



When a soft-stemmed plant is wounded, the place heals over, or to 

 be more accurate, it is covered with a layer of cork. The raised 

 letters which we sometimes see on large vegetable marrows or 

 pumpkins advertising the name of the grower are made of cork, 

 produced by scratching the required letters on the fruit when it is 

 young. W T hen seed potatoes are cut up for planting, it is not 

 customary to set them at once, as it is advisable that the wounded 

 surfaces should heal somewhat before being put into the moist 

 ground. In woody plants such as trees, the process of healing is 

 comparatively much slower. If a piece of bark is stripped from 

 such a stem and the wood is laid bare, the living parts that form the 

 annual rings immediately die, and there is nothing left which can 



