178 THE BOOK OF NATURE STUDY 



worts, are closely associated with trees, living on their wood or 

 bark. One of the most common Lichens on trees is the Usnea 

 barbata, sometimes called the Beard or Tree Moss. It flourishes 

 on old birches and pines, clothing them with a shaggy grey fleece 

 (Fig. 38). The smooth bark of the Holly is often covered with 

 black lines, looking like Hebrew writing ; this is the Lichen, Gr aphis 

 elegans. Lichens are most abundant on trees in those parts of 

 the country where the towns are not only small but infrequent, 

 as in Somerset and Gloucestershire, for they thrive best in pure 

 country air. On the Oak and other forest trees a Lichen which 

 is supposed to resemble the tissue of the lungs is often found; 

 this is Sticta pulmonacea. 



On the ground at the base of the trunk of trees the Grey 

 Trumpet Lichen frequently occurs in dense colonies. It is inter- 

 esting to note that these Lichens often follow each other in a 

 regular order ; certain species frequent young twigs, certain 

 others drier and more exposed branches. Others, again, belong 

 entirely to the oldest branches. In our latitudes the organisms 

 living on bark are almost entirely confined to non-flowering 

 plants ; in the tropics there are many Orchids and plants belonging 

 to the Fig tribe which make their home on the bark of trees. 



In woods there is also a definite fungus flora, which differs 

 according to the dominant tree, no doubt partly owing to the 

 difference in the humus. It has been suggested that fungi with 

 coloured spores are more generally characteristic of Pine woods ; 

 whilst the white-spored species predominate in Oak and other 

 woods of broad-leaved trees. The so-called "Cup Fungus " 

 (Peziza) is a fungus growing on dead sticks in woods about 

 Christmas time. The cup is red. 



The Agarics form a very important group of Fungi. They 

 include Mushrooms and Toadstools. The Fly Agaric is a par- 

 ticularly handsome species, not infrequently to be found under 

 Birch trees (see Plate) . Its cap is scarlet ; the gills on the under 

 surface are white, and in this species a ring of tissue left below 

 the cap is very clearly seen attached to the stem. In autumn 

 a large number of different Agarics are found in woods on dead 

 logs and old stumps. 



Certain Mosses grow on the bark of trees, especially along the 



