90 THE OPEN AIB. 



these, too, are numerous. Then there are the moths, 

 and those creeping creatures that work out of sight, 

 boring their way through the rafters and beams. 

 Sometimes a sparrow may be seen clinging to the bare 

 wall of the house ; tits do the same thing. It is sur- 

 prising how they manage to hold on. They are taking 

 insects from the apertures of the mortar. Where the 

 slates slope to the south, the sunshine soon heats them, 

 and passing butterflies alight on the warm surface, and 

 spread out their wings, as if hovering over the heat. 

 Flies are attracted in crowds sometimes to heated 

 slates and tiles, and wasps will occasionally pause 

 there. Wasps are addicted to haunting houses, and, 

 in the autumn, feed on the flies. Floating germs 

 carried by the air must necessarily lodge in numbers 

 against roofs ; so do dust and invisible particles ; and 

 together, these make the rain-water collected in 

 water-butts after a storm turbid and dark; and it 

 soon becomes full of living organisms. 



Lichen and moss grow on the mortar wherever it 

 has become slightly disintegrated ; and if any mould, 

 however minute, by any means accumulates between 

 the slates, there, too, they spring up, and even on the 

 slates themselves. Tiles are often coloured yellow 

 by such growths. On some old roofs, which have 

 decayed, and upon which detritus has accumulated, 

 wallflowers may be found ; and the house-leek takes 

 capricious root where it fancies. The stonecrop is 

 the finest of roof-plants, sometimes forming a^ broad 

 patch of brilliant yellow. Birds carry up seeds and 

 grains, and these germinate in moist thatch. 

 Groundsel, for instance, and stray stalks of wheat, 



