[OGRAPHICAL MEMORANDA 



practice. His negative attitude was based on a simple and convincing 

 argument. Consider, he had said, two almond trees, one producing 

 sweet, the other one bitter almonds. Obviously these two specimens 

 exhibit a physiological difference that is as striking as it is constant. 

 Nevertheless, no botanist would ever be induced to regard these 

 trees as different species. And what guarantee was there that physiol- 

 ogical differences between two types of bacteria were any more sig- 

 nificant than those exhibited by the two almond trees? Now if, for 

 these reasons, it appeared ill-advised to use physiological charact- 

 eristics for the differentiation of species, how much more forcibly 

 would the argument apply to Winogradsky's and Beijerinck's genera! 

 Furthermore, one might legitimately ask whether such differences 

 were constant. Also in this respect the dangers were certainly not 

 imaginary; it need but be pointed out that Beijerinck himself had 

 shown how easily a strain of luminous bacteria may permanently lose 

 its ability to emit light; this happens, for example, if it is cultivated at 

 moderately high temperatures, where growth is not adversely affected. 

 This implies that such a modified strain would henceforth have to be 

 identified as a member of a different genus ! 



Despite this criticism many of the above-mentioned genera have 

 been perpetuated, largely because they proved to be so eminently 

 useful. No doubt this argues strongly for the thesis that Winogradsky 

 and Beijerinck both had a highly developed 'taxonomic intuition'. 

 Later studies have shown that many of their genera represent assem- 

 blages of organisms with a considerable number of common, more or 

 less basic properties. And spurred on by the example set by the two 

 great general microbiologists, the tendency to employ physiological 

 characteristics in bacterial systematics gradually spread. In view of the 

 paucity of morphological properties and the obvious need for more 

 refined supplementary means of differentiation, this was inevitable. 

 The most elaborate and consistent use of generic names for groups of 

 bacteria with similar physiological properties was made by Orla- 

 Jensen in his attempt to construct a system of bacterial classification 

 that was purported to reflect the phylogenetic relationships of these 

 microbes. He began by recognizing two morphologically distinct lines, 

 represented by the orders Cephalotrichinae and Peritrichinae, comprising 

 the bacteria with polar and peritrichous flagella, respectively; non- 

 motile bacteria were, somewhat arbitrarily, assigned to one or the 



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