M. C. COOKE ON THE DUAL-LICHEN HYPOTHESIS. 177 



hence, as they are out of place in Lichens, they must be unicellular 

 Algae. 



Any one who has had any experience amongst the low forms of 

 vegetable life, in which the organism consists of a single cell, are 

 exceedingly well aware that it is almost an impossibility, from the 

 observation of these cells, to arrive at any satisfactory conclusion as 

 to what they are, and what their ultimate development may be. Let 

 them compare, if they please, what are known to be the earliest 

 stages of Mosses and Algae with the gonidia of Lichens, and draw 

 up characteristic diagnoses, if they can. All are globose cells con- 

 taining a greenish protoplasm, and about equal in size. By what 

 occult power can the theorists distinguish that which, it is admitted, 

 they cannot describe ? Yet the best and most experienced Algalo- 

 gists affirm that of all these forms the gonidia of Lichens are the 

 most distinct and permanent in their character. 



The only safe method by which these low forms can be deter- 

 mined, is by watching their development. In their simple condition 

 of cells they are no more than mere buds, the ultimate form of which 

 only the rash or foolish would predicate. 



If the gonidia of Lichens are true Algae, it is insufficient to state 

 that they so closely resemble Algae that they might be mistaken for 

 such ; there must be some undoubted evidence produced that they 

 are Algae in fact, and not in appearance. 



Nylander, on the contrary, holds that they are organs belonging 

 to the Lichen. He says, " I have adduced that the gonidia and 

 gonimia of Lichens constitute a normal organic system necessary, 

 and of the greatest physiological importance, so that around them 

 we behold the growing (or vegetative) life chiefly promoted and 

 active." Again he says, " The absurdity of such an hypothesis is 

 evident from the very consideration that it cannot be the case that 

 an organ (gonidia) should at the same time be a parasite on the body 

 of which it exercises vital functions."* 



Now, it must be admitted that Dr. Nylanderis the facile princeps 

 of Lichenologists. If it can be shown that these green cells perform 

 an active part in the life of the lichen — in fact, that they are organs 

 possessed of certain functions, then they cannot at the same time be 

 foreign to the plant in which they occur. Nylander has shown that, 

 whenever they are few in number, a proportionate decrease of vitality 



* Nylander, in " Grevillea," ii., p. 146, 147. 



