92 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



here be so primitive that they can hardly be expected to serve as a useful 

 guide in determining phylogenetic trends and relationships. Haeckel, realizing 

 this, had had recourse to physiological properties as well, a practice which led 

 him to incorporate the bluegreen algae, as photosynthetic organisms, in the plant 

 kingdom. As a result, the views of Cohn in respect to the close affinity between 

 the bacteria and the bluegreen algae did not come to a clear expression in 

 Haeckel's system. 



Since it was Cohn who, in 1872, took the most significant steps toward the 

 development of a more detailed classification of the bacteria, it is understandable 

 that in these attempts he adhered to his notion that the bacteria are bona fide 

 members of the plant kingdom. And Cohn's influence has been so great that for 

 a long time Haeckel's proposal was not seriously considered, at least by the bac- 

 teriologists. 



But Copeland, in an important contribution, reexamined the arguments in 

 favor of Haeckel's ideas and conceded their soundness (1938, p. 384) : 



It is an ancient and familiar hypothesis, too widely accepted as a law of nature, that 

 every living creature is and must be either a plant or an animal. Judged by knowledge 

 and theory which were available to Linnaeus, this hypothesis is sound; judged by mod- 

 ern knowledge and theory, it seems untenable. 



As he further pointed out (ibid.) : 



Various authors more recent than Haeckel have shown a disposition to recognize 

 more kingdoms than two, but none of them, apparently, has formulated a system includ- 

 ing all organisms. Pending such an accomplishment, the old system of two kingdoms 

 has persisted for want of a workable substitute. 



With a view to improving this situation Copeland developed a substitute in which 

 four kingdoms were recognized: Monera, Protista, Plantae, and Animalia. The 

 first phylum of Haeckel's Protista was here raised to the rank of an independent 

 kingdom, the criterion for inclusion in this taxon being "organisms without 

 nuclei, the cells solitary or physiological (ly) independent. Groups included, 

 bacteria and bluegreen algae" (p. 416). In this manner a seemingly unambigu- 

 ous separation of the bacteria and bluegreen algae from all other organisms w^as 

 achieved, while at the same time justice was done to Cohn's concept regarding 

 the close relationship between the two major groups of the Monera. 



Several years later Copeland returned to the problem of basic classification. 

 At this time he stated the phylogenetic significance of the first kingdom more 

 clearly, as follows (1947, p. 342) : 



The most profound of all distinctions among organisms is that which separates those 

 without nuclei from those which possess them. The foi'mer are the bacteria and blue- 

 green algae. . . . Whether or not life originated more than once, it is certain that life 

 possessing nuclei came into existence once only, by evolution from "tionnucleate life. 

 This conclusion is as certain as any which can be based on induction: it is established 

 by the uniformity of the nucleus, in its structure and in its behavior, in mitosis, in 

 sexual reproduction, and as the vehicle of Mendelian heredity, wherever it occurs. 



He also recognized that his designation of the kingdom as Monera was invalid 

 because Enderlein (1925) had earlier used the name Mychota for just such a 

 taxon. Meanwhile, the proposition of uniting the bacteria and bluegreen algae 

 in a separate kingdom had found favor with Stanier and van Niel (1941), who 

 had, furthermore, seen fit to expand the characterization of this unit by the 



