2i6 Transactions British Mycological Society. 



to evanescent morphological facies, but the concentration of 

 energy in the discovery of suitable breeding technique. The 

 results obtained in the cultural treatment of organisms patho- 

 genic to man must here be an mspiration. 



Attention is most usually drawn to the Hymenomycetes and 

 the application of a physiological concept of species in their 

 systematic treatment derided; the opinion being expressed 

 that although the lower fungi may be plastic, such groups as 

 the Agaricineae, Polyporeae, etc. contain species well defined 

 and constant, whose specific purity may be determined by 

 morphological comparison alone. It is extremely improbable 

 that this is true. In the Agaricineae are a very great number of 

 growth forms which have been studied so minutely and patiently 

 and their essential descriptive characters placed on record so 

 fully, that few possible permutations or combinations of 

 morphological characters can remain unreported. This huge 

 assemblage of forms has been arranged by certain artificial 

 criteria so that whenever a growth form is examined it may be 

 relegated to one or other of the almost innumerable diagnoses 

 in existence. These diagnoses are regarded as distinctive of 

 species but their true value is that of "ecad" descriptions. 

 If reference be made to the diagram, the diagnoses do not 

 appl}^ to the species i, 2, 3, 4 and so on, but to the growth forms 

 k, m, I, a, etc. Any one of the species i, 2, 3 under certain 

 conditions will produce growth forms fitting a particular 

 diagnosis. If, however, species 2 under environmental con- 

 ditions E gives rise to a growth form which has not already been 

 described, a new diagnosis is drawn up fitting the new "species." 



If, however, the particular growth form is the morphological 

 expression of the resultant of the interaction of the physio- 

 logical constitution of the organic individual, and the special 

 environmental conditions, and it is extremely difficult with 

 the evidence at our disposal to conceive what else it can be, 

 then it follows that under certain conditions, like resultants 

 may be produced by unlike physiological constitutions. Thus 

 even in the higher fungi there is no reason to suppose that under 

 the influence of the infinitely variable environmental conditions 

 the phenomena of morphological convergence and divergence 

 are not operative. In such case it does not necessarily follow 

 that two similar morphological entities which may receive 

 the name Hydnum repandum or Agariciis melletis might not 

 possess totally different physiological constitutions which under 

 other conditions of growth would diverge characteristically. 

 While therefore it is interesting to possess the detailed knowledge 

 which has been accumulated regarding the growth forms of 

 the higher fungi, it must always be realised that the so-called 



