THE STORY OF THE LICHENS 109 



serving moisture for the enslaved algae. It 

 has been intimated that many species of algae 

 which have been discovered in the lichen alli- 

 ance may be found supporting a separate 

 existence. Time and again the experimenter, 

 in isolating the green cells from the lichens, 

 has discovered that the little plants were iden- 

 tical with well-known algae which had been 

 named and known for many years. 



Undoubtedly these algae are the most 

 omnipresent of all kinds of vegetation. The 

 waters of the world are full of them, and 

 the same may be said for the atmosphere and 

 the earth. So small are they, however, that 

 it is only when they occur in vast numbers, 

 such as on the surface of rocks or barks of 

 trees, that we are aware of their presence at 

 all in the ordinary way. Then they appear as 

 somewhat slimy coatings, more or less green 

 in colour. In a dry state algae float about in 

 the air and do not seem to suffer in the very 

 least from a prolonged period of inactivity. 

 With the arrival of moist conditions the minute 

 plants settle down and resume their normal 

 method of growth. When the wonderful powers 

 of adaptation in the algae are considered, side 



