VI The Web of Life 115 



than these. Their immense variety has given no small 

 amount of labour to the systematists, and a well-developed 

 specialism of " lichenology " with a literature and with 

 collections voluminous enough to surprise any one who first 

 enters upon it, has arisen in consequence. In 1866 the 

 penetrating cryptogamist De Bary threw out the suggestion 

 that the many resemblances shown by the lichens on one 

 hand to fungi and on the other to algae, might really be 

 due to an admixture of these two constituents. The idea 

 was taken up and worked out carefully by his pupil 

 Schwendener, to whose practical insight and industrial 

 training the science owes other important ideas. 



From the fungus-like tissue of a lichen he isolated little 

 greenish cells like Protococcus and other unicellular algae, 

 and in some cases these green cells were able to live and 

 multiply after they had been isolated. This remarkable 

 fact led Schwendener to develop the hint given by De Bary, 

 and to establish his so-called " dual hypothesis " of the 

 nature of lichens. 



"As the result of my researches," he says, "all these 

 growths (lichens) are not simple plants, not individuals in 

 the ordinary sense of the word ; they are rather colonies 

 consisting of hundreds and thousands of individuals, among 

 which, however, one predominates, while the rest in perpet- 

 ual captivity prepare the nutriment for themselves and their 

 master. This master is a fungus, a parasite which is 

 accustomed to live upon others' work ; its slaves are green 

 algae, which it has sought out, or indeed caught hold of 

 and compelled into its service. It surrounds them, as a 

 spider its prey, with a fibrous net of narrow meshes, which 

 is gradually converted into an impenetrable covering ; but 

 while the spider sucks its prey and leaves it dead, the 

 fungus incites the algae found in its net to more rapid 

 activity, indeed to more vigorous increase." 



