156 



THE NATURE BOOK 



orange and browTi. The midrib runs direct 

 to the apex, the side ribs branch right 

 and left, and terminate in the larger 



GALLS ON BIRCH TWIGS. 



serrations at the margin. The stalks of 

 the leaves are comparatively long, about 

 half as long as the midrib, and give a 

 delicate poise. The leaves scarcely hide 

 the tree's framework, and cast but a slight 

 shadow. 



The flowers, pollen-bearing and fruit- 

 producing, are separate, but to be found 

 on the same tree. They are both crowded 

 into cylindrical catkins. The pollen- 

 bearing catkins make their appearance 

 in August, and remain in position all 

 the winter through, stiffly erect in rela- 

 tion to the twigs which they terminate. 

 In the spring they elongate, and fall 

 over, hanging loosely pendulous, ready 

 for the wind to shake out and scatter 

 their pollen dust. All through the 

 winter the fruit-producing catkins are 

 safely packed away in the lateral buds 

 of the twigs, and emerge erect with the 

 leaves in the spring. 



The fruit has the appearance still 

 of a catkin, for the erect flower-catkin, 

 lengthening slightly, has turned itself, 

 pointing downwards. It now suggests a 

 stiffish rounded tassel of threaded discs, 

 though these discs are really elongated 

 scales with wings so arranged that their 

 combined edges become circular. When 

 fully ripe, well on in the winter, these 

 scales drop off, setting free the tiny seeds, 

 and leaving exposed the central stalk, 

 or thread, of the catkin, which remains 

 long on the twig. The seeds have two 



round transparent wdngs, or sails, present- 

 ing considerable surface to the wind by 

 which their dispersal is secured. 



A rather frequent gall found on this tree 

 is that caused by the Birch gall mite, 

 a similar insect to that which affects 

 so disastrously the Black Currant buds 

 in our gardens. The buds infested by 

 this mite either do not open or expand 

 irregularly. 



Another abnormal growth, and one 

 that is peculiarly disfiguring to this tree, 

 is that known commonly as " The Witch's 

 Broom," a crowd of short twigs in- 

 extricably involved and massed, which 

 grow eventually to a great size. By some 

 this is said to be the result of the tree's 

 efforts against the crippling action of the 

 gall mites referred to above ; but it is also 

 explained as due to similar efforts against 

 th'3 mischievous ramifications of a minute 

 fungus. 



THE HORNBEAM. 



The Hornbeam stands in sharp contrast 

 with the Birch. In its younger stages, 

 at least, it well endures if it does not 

 show a ]')reference for shade. It casts 



TRUNK AND BARK OF THE HORNBEAM. 



