LICHENS 137 



for either to exist at all by itself. It is possible to grow each 

 separately, but only in artificial conditions. How, then, it may be 

 asked, do the algae and fungi meet one another ? Are not the 

 chances against the spores of the alga meeting with those of the 

 fungi very great. It must be realised, however, that the algae, 

 which help to form the lichens, are not the long green threads which 

 occupy our pools and ponds, but minute green bodies of very 

 minute size, which are only noticed in places where their myriad 

 numbers attract attention, such as the green on old palings and 

 bark of trees. These can dry up without harm and form a 

 powder which can be blown great distances by winds of moderate 

 strength. As to the fungus, everybody knows that the spores of 

 various kinds are everywhere present in the air ; otherwise, how 

 do moist surfaces so soon become "mouldy." If the nature student 

 wishes to convince himself of the fact that the spores of both algae and 

 fungi are present in the air, it is not difficult to do so. In many places, 

 but especially in mountain valleys, evidence may soon be procured. 

 Nail a sheet of coarse filter paper to a board, keep it moist, and 

 expose it for a few hours when a moderate wind is blowing. The 

 microscope will show that sticking to the paper are the spores of 

 many algae, mosses, and fungi, together with particles of dust and 

 the pollen grains of flowering plants. In the same way these spores 

 come to rest in grooves and irregularities on the surface of rocks 

 and soon germinate, the algae spores into little cell groups, and the 

 fungus spores into interlacing masses of threads ; the former are 

 embraced by the latter and the confederacy produced which we call 

 a lichen. 



The collection and identification of lichens will not be an easy 

 task, but some of the common kinds should be examined by the 

 nature student, to whom for further points in this remarkable group 



