CONSTANCE. SYSTEMATICS OF THE ANGIOSPERMS 407 



is well known. Hence arises its superiority over arbitrary or artificial systems, such as 

 that of Linnaeus, in which there is no combination of ideas, but which are mere collec- 

 tions of isolated facts, not having any distinct relation to each other. . . . This is the only 

 intelligible meaning that can be attached to the term Natural System, of which Nature 

 herself, who creates species only, knows nothing. It is absurd to suppose that our genera, 

 orders, classes, and the like, are more than mere contrivances to facilitate the arrange- 

 ment of our ideas with regard to species. A genus, order, or class is therefore called 

 natural, not because it exists in Nature, but because it comprehends species naturally 

 resembling each other more than they resemble anything else. 



The era of natural systems of classification had its culmination in the Genera 

 Plantarum of Bentliam and Hooker (1862-1883), which did not attempt to be 

 a new general system. As remarked by Green (1914, pp. 50-4—505), "the chief 

 merits of Bentham and Hooker's great work lie below the surface. It is not until 

 we study the arrangements in the orders and the illuminating treatment of the 

 genera and species that we realize how great it is, and what light it has thrown 

 upon Natural Affinities." The work frankly follows the system of de Candolle, 

 since there appeared to be no better alternative at the time, and this system 

 was widely known. 



In addition to their general similarity in the arrangements of groups, all 

 the natural systems agreed in being based upon two fundamental concepts: (1) 

 the efficacy of structural similarity as the true guide to affinity and hence proper 

 arrangement, and (2) the special creation and immutability of species. De Can- 

 dolle wrote (Candolle and Sprengel, 1821, pp. 95-97) : 



By Species {species), we understand a number of plants, which agree with one another 

 in invariable marks. In this matter everything depends upon the idea of invariableness. 

 . . . This idea proceeds on the supposition, that the species which we know, have existed 

 as long as the earth has had its present form. No doubt there were, in the preceding 

 state of our globe, other species of plants, which have now perished, and the remains of 

 which we still find in impressions in shale, slate-clay and other floetz rocks. Whether 

 the present species, which often resemble these, have arisen from them; — whether the 

 great revolutions on the surface of the earth, which we read in the Book of Nature, 

 contributed to these transitions, — we know not. What we know is, that from as early a 

 time as the human race has left memorials of its existence upon the earth, the separate 

 species of plants have maintained the same properties invariably. To be sure, we fre- 

 quently speak of the transitions and crossings of species; and it cannot be denied that 

 something of this kind does occur, though without affecting the idea of species which 

 we have proposed. . . . Nature seems to prevent the mutual impregation of related 

 species in more ways than one, although these are not completely understood by us. 



In Germany, where the natural systems had made comparatively little head- 

 way against the Linnaean, the pendulum swung in about 1840 from exclusive 

 preoccupation with "the old and foolish notion, that the sole or chief business 

 of every botanist is to trifle away time in plant-collecting in wood and meadow 

 and in rummaging in herbaria" (Sachs, 1890, p. 187), to more fundamental but 

 hitherto undeveloped phases of plant science. Sachs credits Schleiden with lead- 

 ing the shift in emphasis to the inductive viewpoint that at once changed botany 

 from the status of a purely descriptive to that of a truly natural science, on the 

 same basis as chemistry or physics. Of more immediate importance to syste- 

 matics, however, were the revival of anatomical investigation by von Mohl and 

 the elaboration of cell formation by Niigeli, although their researches were di- 

 rected chiefly to cryptogams. Such studies as these paved the way for Hof- 



