THE NATURE OF THE ASSOCIATION OF ALGA 

 AND FUNGUS IN LICHENS. 



BY GEORGE JAMES PEIRCE, 

 Assistant Professor of Plant- Physiology, Leland Stanford Junior University. 



CONTENTS. 



Page. 



Plate XLI. 



I . Introduction 207 



II. The Germination OF Spores 211 



III. The Relations of Gonidia and Hyph^ as shown by 



Cultures 216 



IV. The Relations of Gonidia and Hyph^ as shown by 



Microtome Sections 221 



V. The Significance of the Water-content of Ramalina 



reticulata 229 



VI. The Influence of Mechanical Strains on Growth 231 



VII. Nucleus or Pyrenoid as the Central Body of Cysto- 



coccus Cells 234 



VIII. Summary 236 



Bibliography 239 



Explanation of Plate 240 



I. Introduction. 



The last few years have seen a revival of interest, grati- 

 fyingly widespread, in the study of lichens. Except during 

 the few years immediately following the writings of DeBary, 

 Schwendener and Reinke, which wrought a revolution in 

 our conception of lichens, they have been studied mainly by 

 systematists. These found in macroscopic characters all 

 that was required to determine an old or to describe a 

 new species. Every one must have felt, even before Reinke 

 recently recalled the question so forcibly to the minds of 

 botanists, that by no means the last word had been said 

 about these interesting organisms, and that the study of 



[207] May 13, 1899. 



