MICROSCOPICAL STRUCTURE OF LICHENS. 169 



and description of these puzzling organisms very often to the 

 exclusion of research into their microscopic structure. This 

 field of research is open to the worker who will bring to bear on 

 the subject the necessary skill in microscopical manipulation. 



Summary of Results. 



1. The gonidium of a large number of British lichens is most 

 probably a species of Chlorella. 



2. The gonidium does not divide vegetatively, but sporulation 

 takes place within the algal mother cell while it forms a con- 

 stituent of the lichen thallus. 



3. The sporulation is similar to that which takes place within 

 free Chlorella cells. 



4. Penetration of living gonidia by hyphae seldom, if ever, takes 

 place. 



5. The percentage of dead empty gonidial cells within the lichen 

 thallus is as a rule quite small. 



6. In a well-developed lichen the gonidia have all the appear- 

 ance of being thoroughly healthy. 



Bibliography. 



(1) Bonney, Victor : A New and Rapid Triple Stain, Archives 



Middlesex Hospital, vol. xiii. 1908. 



(2) Danilov, a. N. : Ueber das gegenseitige Verhaltnis zwischen 



den Gonidien und dem Pilzkomponenten in der Flechten- 

 symbiose. Bull. Jard. Imp. Bot. Petersbourg, tom. x., livr. 

 (2) 1910. Translation in Journal of Botany, vol. Ivi. June 

 1918. 



(3) Paulson, R., and Hastings, Somerville : Relation between 



the Alga and Fungus of a Lichen, Journ. Linn. Soc, Botany, 

 vol. xliv. March 1920. " 



(4) Peirce, G. I. : The Nature of the Association of Alga and 



Fungus in Lichens, Proc. Calif. Acad. Sci. Bot., vol. i. 1899. 



(5) ScHWENDENER, S. : Die Algentypen Flechtengonidien. Basel, 



C. Schultze. 1869. 



