170 THE JOURNAL OF BOTANY 



according to the late Prof. M. S." Voronin, they certainly gave the 

 impression that the hyphie develop algal cells. 



The question is one of extreme interest. Acting at the suggestion 

 of A. A. Elenkin and with his closest assistance in the spring of 1909, 

 I made observations with a view of ex])laining what Elf ving had seen 

 in his preparations, as he had apparently obtained a sufficient founda- 

 tion for the publication of conclusions entirely opposed to the views 

 on the nature of lichens strongly held since the time of Schwendener, 

 viz. a fungus in symbiotic relationship with an alga. 



Before we come to the explanation of the facts observed, it will 

 not be superfluous to indicate the materials on which my investiga- 

 tions were made. From the 20th April to the end of May, material 

 was being collected in the neighbourhood of St. Petersburg, and 

 afterwards throughout the whole summer in the Vitebsk province — 

 an interval of two weeks occurred between the former and the latter 

 collections. The observations were made principally on Evernia 

 prunastri and E. fiirfuracea. In addition, the following were also 

 examined for purposes of comparison : Farmelia sulcata, Ramalina 

 farinacea, Usnea harhata, Cladonia rangiferina, Xantlioria parie- 

 tina, Lecanora angulosa, and also the separately growing Cliloro- 

 coccum. Part of the material obtained was fixed, immediately after 

 collection, in 75 "/o oi" i" absolute alcohol. 



The first observations were made on sections cut with a razor, both 

 from fresh material and from that fixed in spirit. The material was 

 prepared for examination by being put through absolute alcohol and 

 xylol and was embedded in paraffin ; the sections varied from 1 // to 

 15 fji. in thickness ; the 1 /x. sections were however unsatisfactory, but 

 fully satisfactory results were obtained from the 2 ^ sections. Some 

 of the sections, stained and unstained, were examined in a liquid 

 medium, water or glycerine. In such cases the following method 

 was employed in every instance : the section was first examined as a 

 whole, then broken up under a cover glass, by careful tapping and 

 pressm-e, in order that the separate hyphte and gonidia might be 

 observed more minutely. Various stains were used — carmine, fuchsin, 

 methyl gi-een, methyl blue, safranin, lijematoxylin. Of these the 

 most suited to my purpose were a mixtvire of fuchsin and method 

 green, made acid with acetic acid. During both staining and clearing, 

 the preparations were kept on slides in beakers filled with the same 

 solutions as those used for staining in bulk. I at first washed with 

 spirit of a different strength, but found it very difficult to ascertain 

 the precise moment at which to cease washing, for decolouration 

 takes place very rapidly when the spirit is either too strong or too 

 weak. Spirit greatly diluted with water I found impossible to use 

 for the work, as the preparations would absorb too much water and 

 become impossible to fix. For this reason I began to use a solution 

 of glycerine in strong spirit. In this solution decolouration proceeds 

 less rapidly and thus gives a better opportunity to cease washing at 

 the moment when the differentiation of the various parts of the 

 preparation has attained its greatest distinctness. The fixed sections 

 were mounted in glycerine jelly and the mifixed ones in glycerine. 

 The most interesting preparations were examined with a Zeiss apo- 

 chromatic objective magnifying 1000 diameters. 



