Some Concepts in Mycology. William B. Brierley. 207 



But even when plasticity has been recognised, the problem 

 of systematic categorisation is not by any means rendered 

 simple for there is still the question of specific variability. 

 The variability of many phanerogamic species has been shewn 

 to be due to the fact that the species group really consists of 

 two or more elementary or Jordanian species as in the well- 

 known cases of Draba verna, Capsclla hursa-pastoris, Solanitm 

 nigrum, etc. Each of these little species may itself be plastic. 

 Furthermore it is very probable that many elementary species 

 may consist of two or more of Johannscn's(iy)/)z^;'c Zwesseparated 

 from each other by qualitative chemical differences, each pure 

 line being itself plastic*. Moreover not only may external 

 causes bring about the production of different morphological 

 facies in specimens of the same species, but inversely the 

 essential differences of two or more elementary species may 

 themselves disappear under the influence of certain environ- 

 mental conditions. For example, the pink colour of the 

 corolla of certain elementary species of Primula sinensis may 

 be eliminated by growing the plants at a higher temperature, 

 and the resulting white forms may then no longer be dis- 

 tinguished from elementary species characterised by the 

 possession of white corollas. The same phenomena may be 

 brought about with the blue corolla of certain Campanulas, 

 or the red colour of the copper beech which may be eliminated 

 by development in deep shade. And complicating all these 

 things is the gametic condition of the organism and the 

 discovery of Nilsson-Ehle(3i) that a pure line may be homo- 

 zygous in respect to one character and heterozygous in respect 

 to another. 



In the phanerogams the different species are distinguished 

 by many characters; units each of which may be investigated 

 separately. And yet even this very brief indication of some 

 of the difficulties involved in the systematic treatment of such 

 plants will serve to shew that the prevailing morphological 

 species-concept depending upon the "systematische blick" is 

 far from being finally satisfactory. 



When, however, we attempt to apply this concept to the 

 already known facts of mycology and to the everyday laboratory 

 and field experience of the experimentalist we create a total 

 impasse. 



An adequate review of the literature cognate to this subject 

 is not feasible here. As however the most critical descriptive 

 character in the systematic treatment of fungi is the reproductive 

 body, attention may be drawn to a few of the more recent 



* "Each animal and vegetable species differs strictly from all others by the 

 chemical composition of its living substance." (MacLeod 24, 2.) 



9—2 



