4 ] The Classification of Lower Organisms 



from the attempt to formulate a definite and comprehensive system. This teaching 

 was the original stimulus which has led to the present work. I bear witness that E. B. 

 Copeland taught these things in 1914; he did not publish them until he had ceased 

 to teach (1927). 



In the year 1926, when the teaching of elementary botany was first fully my own 

 responsibility, I came to the conclusion that the establishment of several kingdoms 

 of nucleate organisms in addition to plants and animals is not feasible; that all of 

 these organisms are to be treated as one kingdom. This is one of the few points of 

 originality which I claim for my work. It is true that the kingdom thus described is 

 not very different from the third kingdom which various early authors proposed and 

 which Haeckel (1866) named Protista. Haeckel, however, in his varied presentations 

 of the kingdom Protista, included always the bacteria. By setting apart the bacteria 

 and blue-green algae as yet another kingdom, one meets, at least in part, the objection 

 to the "third kingdom" that it is heterogeneous beyond what can be tolerated. 



It has been necessary to meet also the objection that the "third kingdom" substi- 

 tutes, for an acknowledgedly vague boundary between plants and animals, two vague 

 boundaries: it has been necessary to recognize characters by which sharp definition 

 can be given to plants and animals. It is my contention that these characters have 

 long been known. The kingdom of plants, as the taxonomic representation of a 

 natural group, is to be defined by the system of chloroplast pigments described by 

 Willstatter and Stoll (1913), and also by the production of certain carbohydrates 

 which occur only sporadically elsewhere. The kingdom of animals is defined by em- 

 bryonic development through the stages called blastula and gastrula, as pointed out 

 by Haeckel (1872). It is believed that no organisms exhibit both of these sets of 

 characters; the "third kingdom" includes the nucleate organisms which exhibit 

 neither. The kingdoms of plants and animals as here defined are essentially those 

 which are traditionally and popularly accepted. They include all the creatures which 

 Linnaeus listed as plants and animals, with the exceptions of forms of which he knew 

 little, and which he listed superficially at the ends of his treatments of the respective 

 kingdoms. 



Of course, the definitions are not warranted to describe the kingdoms without ex- 

 ception. For one thing, each is supposed to have come into existence by evolution 

 through a line of organisms which exhibited its characters imperfectly. For another, 

 evolution can erase what it has created; it is proper to include in a group organisms 

 which have by degeneration lost its formal characters. These things are true of all 

 taxonomic groups. 



In due form, then, the system of kingdoms here maintained is as follows: 



Kingdom I. Mychota. Organisms without nuclei; the bacteria and blue-green 

 algae. 



Kingdom II. Protoctista. Nucleate organisms not of the characters of plants and 

 animals; the protozoa, the red and brown algae, and the fungi. 



Kingdom III. Plantae. Organisms in whose cells occur chloroplasts, being plastids 

 of a bright green color, containing the pigments chlorophyll a, chlorophyll h, carotin, 

 and xanthophyll, and no others; and which produce sucrose, true starch, and true 

 cellulose. 



Kingdom IV. Animalia. Multicellular organisms which pass during development 

 through the stages called blastula and gastrula; typically predatory, and accordingly 

 consisting of unwalled cells and attaining high complexity of structure and function. 



This system has twice been given brief publication (1938, 1947). I am glad to say 



