406 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



must be acquainted with the relative importance which belongs to organs, compared with 

 one another; in the second place, we must know the circumstances which might lead the 

 observer to mistake the true nature of organs; and, in the third place, we must be able 

 to estimate the importance which may be attached to each of the points of view, under 

 which an organ may be considered. 



Morphology of reproductive structures — seeds, fruit, flowers — was asserted to 

 furnish a reliable basis for determining affinity, and a warning was issued 

 against employing for this purpose physiological characters vital to the func- 

 tioning of the plants. Abortion, alteration, and union of organs were empha- 

 sized as the three basic causes likely to confuse the observer by concealing basic 

 symmetry and hence true affinity. De CandoUe (1844) distinguished dicoty- 

 ledons and monocotyledons, and then divided the former into choripetalous- 

 hypogynous and perigynous-epigynous, sympetalous, and apetalous (including 

 gymnospermous) lines, respectively. Sympetalous types, notably Compositae, 

 were regarded as the climax of the system. In espousing this arrangement, 

 Hooker said (1873, p. 994) : 



The Cohorts may thus be fancifully likened to the parti-coloured beads of a necklace, 

 joined by a clasp, the beads touching at similarly coloured points of their surfaces. The 

 position of each bead in the necklace is determined by the predominance of colours com- 

 mdn to itself and those nearest to it; whilst the number and proportion of the other 

 colours which each bead presents, indicates its claims to be placed elsewhere in the 

 necklace; in other words, such colours represent the cross affinities which the Cohorts 

 display with others remote from the position they occupy. 



Endlicher (1836-1840) proposed a similar arrangement, but regarded the 

 choripetalous Leguminosae as capping his scheme; incidentally, he erred in plac- 

 ing cycads and the parasitic and reduced Balanophoraceae and the genus Cy- 

 tinus among the vascular cryptogams. Brongniart's system (1843) is notable 

 chiefly for the attempt to break up the unisexual and/or apetalous dicotyledons 

 and insert them among choripetalous ones. The arrangement of A. de Jussieu 

 (1850) placed monocotyledons before dicotyledons, and within the latter showed 

 a sequence of sympetalous, choripetalous, and gymnospermous orders. By 1873, 

 J. D. Hooker was able to state his acceptance of the following propositions: (1) 

 that the primary division of the vegetable kingdom is into cryptogamic verus 

 phanerogamic plants; (2) that the primary division of phanerogams is into 

 dicotyledons versus monocotyledons; (3) that the primary division of dicoty- 

 ledons is into angiosperms versus gymnosperms; and (4) that the perianth must 

 be resorted to for further grouping, both in dicots and monocots. The first ap- 

 pearance of the natural system in America was marked by the publication of 

 an American edition of Lindley's Introduction in 1831. Torrey and Gray's A 

 Flora of North America (1838-1840), Avas based on the Candollean system. 



The following statement by Lindley (1830, p. xvi) affords us as much infor- 

 mation as we can perhaps expect on the contemporary conception of the meaning 

 of affinity. 



The principle upon what I understand the Natural System of Botany to be founded 

 is, that the affinities of plants may be determined by a consideration of all the points of 

 resemblance between their various parts, properties, and qualities ; and that thence an 

 arrangement may be deduced in which those species will be placed next each other 

 which have the greatest degree of relationship; and that consequently the quality or 

 structure of an imperfectly known plant may be determined by those of another which 



