HOW SEEDS GERMINATE 17 



as the point of a worn plough-share is renewed by 

 the blacksmith. 



9. How the root behaves when the tip is lost. 



The greatest danger to this wonderful root-tip eomes^ 

 not from hard work, but from insects. Many insects, 

 like the wire-worm, the mole-cricket, and the grub of 

 the cockchafer, live as greedily on roots as a cater- 

 pillar lives on leaves. The root-tip is therefore often 

 eaten ; and it is a strange fact that when this happens 

 the root seems to lose its way like an insect that has 

 lost its " feelers." It may grow longer, but it does 

 not, as before, move downwards. But the plant must 

 have downward-roots ; and so new roots spring out 

 of the injured root and grow downwards. Shift a 

 downward-root with a blunt wire so that it points 

 sideways. In a little time, it will begin to point again 

 downwards. Repeat the experiment, having first cut 

 off the tip, and watch what happens. Have you ever 

 noticed that when the top shoot of a pine tree is 

 broken off, one or two of the side branches take up its 

 work and grow upwards ? Compare with this what 

 happens to your injured root. 



Experiments and Exercises. — 



(1) Continue experiments on the seeds mentioned in the last 

 chapter. 



(2) Find an old tree that has thrown up suclcers from the 

 roots. Measure the distance from the stem to the furthest sucker, 

 and compare with the height or reach of the tree. If the tree has 

 "suckered" all round, you can, in this way, see the root-area. 



Note. — Pears, white poplars, elms and some plums often sucker 

 freely. 



(3) Compare the stem of a pine tree with the tap-root of a 

 dandelion or of a mallow weed. 



Composition Exercise. — Write an account of the Root-tip and. 

 its work. 



