678 CONSTANCY AND MUTABILITY OF FUNGI. 



more, however, the methods of pure cultivation have been 

 perfected, the more has the conviction gained ground that 

 such variations in their characters probably occurs to as 

 slight an extent in the case of the bacteria as in that of 

 higher organisms, and that the former observations on which 

 these statements were founded were not made by methods 

 which were free from objection. Buchner himself has in his 

 more recent investigations pointed out numerous specific 

 morphological characters. It is no doubt not impossible that 

 many of the species which have as yet been looked on as 

 definite forms from examination by incomplete means, and 

 at an early period of our knowledge, may, when the modes of 

 investigation have become more perfect, be recognised as 

 related to each other, and that thus from two species which 

 have as yet been looked on as morphologically distinct we 

 may have to form a single species with a somewhat great 

 variability in vegetative form. But as yet no facts of this 

 kind have been demonstrated, and if they should be demon- 

 strated in any individual case they would not afford any 

 ground for doubting the value of the morphological characters 

 in distinguishing the species of other bacteria.* 



2. Physiologi- In view of the difficulty of the morphological dis- 

 )es ' tinction of species, we must, as has already been men- 

 tioned above, in many cases employ marked and specific 

 physiological characters as means of diagnosis and of 

 classification. The characters so employed must 

 naturally be constant and hereditary; it is only then 



* Buchner has recently (Arch.f. Hyg., vol. iii., p. 380) implied that I 

 confound variability in vegetative form with that of species, and that 

 I fight against the former, while in reality I mean the latter. But 

 from various portions of my criticisms of Zopf's hypothesis, as well as 

 in the first edition of this book, it is very evident that I am by no 

 means guilty of any such mistake. As a proof I cite the following 

 passage from p. 276 of the first edition of this work : 



"In spite of the view that cocci, bacteria, bacilli, spirilla, only 

 represent developmental forms which readily pass into each other, it 

 might nevertheless be still possible to form distinct morphologically 

 characterised species. We observe in the cocci, bacilli, and spirilla, 

 many other peculiarities of form which might serve to characterise a 

 species, and if the chief weight were laid on these peculiarities we 

 would obtain a classification founded on morphological characters, and 

 could ultimately attempt to make a diagnosis of the species according 

 to the external form, even though the same fungus occurred in a coccal, 

 bacteric, or spirillar form." 



According to the view which Buchner and Wernich support, such a 

 differentiation of constant forms would not, however, be trustworthy ; 

 these morphological characters would, as a rule, only be the product of 

 the external conditions of life. 



