LICHENS. 79 



It was assumed that the green gonidia were uni- 

 cellular algae, but the assumption was not proved or 

 their independent existence demonstrated ; but it has 

 been shown, on the contrary, that they are a com- 

 ponent part of the lichen-thallus, being definite organs 

 of the lichen, performing definite functions in its 

 behalf. Hence it was contended that where an orga- 

 nism is seen to exist, and continues to reproduce 

 itself in conformity with a certain type, it is folly ta 

 attempt, by multiplying causes, to account for pheno- 

 mena in an abnormal manner which can be readily 

 accounted for by normal causes. When we see an 

 organism in possession of certain organs, which organs 

 perform certain functions however small, and these 

 organs and functions are inherited and transmitted, 

 there is a pretty strong presumption that all our 

 efforts to demonstrate external causes, to account for 

 phenomena already well accounted for, will only 

 embark us on a profitless speculation.^ 



* For further information on this vexed question, consult "The 

 Pual-Lichen Hypothesis," by M. C. Cooke {Grevilka, Marcli, 1879), 

 p. 102; 'joiti-nal of Quckelt Microscopical Club {l^']oi), vol. v. 170. 



