HEDGE AND DITCH 153 



leaf ? Which of the eight trees on our list cast their 

 stipules when the buds open ? Which keep their stipules 

 through the summer ? What is the use of the stipules in 

 each case ? Mention any trees on our list which have 

 compound leaves. How do you distinguish a leaflet of 

 a compound leaf from a simple leaf, and a compound leaf 

 from a number of simple leaves growing on the same 

 spray ? 



Our hedge is mainly a hawthorn hedge, and we must 

 particularly attend to this tree. What is the haw from 

 which it takes its name ? Sometimes the tree is called 

 whitethorn ; do you know of any blackthorn ? (i) 



Hawthorn-trees, if left to themselves, grow tall, and cast 

 a deep shade, which hinders the undergrowth and causes 

 spaces to appear between the trunks. This does not suit 

 the farmer, who wants a close hedge to keep his cattle 

 from straying. How does he treat an overgrown haw- 

 thorn-hedge ? 



Many of the topmost sprays of the hawthorn-hedges 

 around us end in knobs ; what are these knobs ? They 

 cannot be buds, for you will find that they last all through 

 the summer, and in the withered state through the following 

 winter. If you examine them closely, you will find that 

 they are galls, and consist of brown, stunted leaves. The 

 growing tips have been pricked and gnawed, so that they 

 could not grow into straight and regular shoots ; they 

 have done their best to put forth leaves, but some of the 

 leaves have been killed, while others are crowded and dis- 

 torted. What was it that pricked all these growing tips ? 

 The grub of a small two-winged fly, that you could hardly 

 see without a lens. This grub fed on the soft, juicy 

 tissues of the growing shoot until at length it stopped feed- 

 ing, fell to the ground, and entered the earth, where it 

 turned into a pupa ; the pupa turned into a fly, and by 

 midsummer only the distorted knobs remained to show 

 where the flies had been reared. The fly bears a cumbrous 

 name (Cecidomyia crataegi) ; we might call it the hawthorn- 



