STRUCTURAL SIGNIFICANCE OF DIMORPHIC BRANCHES. 9 



dimorphic branches has two kinds of vegetative metamers, in addition 

 to the various kinds of floral or reproductive metamers. In the cotton 

 plant, for example, seven principal kinds of metamers might be 

 enumerated : The two kinds that compose the two types of branches, 

 the two kinds whose specialized leaves form the involucre and the 

 calyx, and the metamers of the corolla, the stamens, and the pistils. 

 Some plants, such as Broussonetia, have two kinds of vegetative 

 metamers alternating in the same stem, each alternate internode 

 having only a small leaf." 



The diversity of the metamers does not end with the recognition 

 of the different types, for the individual metamers of the various 

 groups are often as distinctly different among themselves as the 

 plants they compose, or even more so. If it be considered that a plant 

 is an aggregate or colony of metamers, it follows that causes of dif- 

 ferences between plants are to be sought in the structure or behavior 

 of the component metamers. Plants with dimorphic branches not 

 only have two kinds of vegetative metamers, but have them arranged 

 in separate series. The variations of the higher plants are much more 

 readily appreciable than the variations of the higher animals, because 

 the same character is repeated in the large number of internode indi- 

 viduals that compose the bodies of plants. 



The individuality of the internodes and the significance of this 

 fact in the developmental history of plants were appreciated over a 

 century ago by Goethe, the great German naturalist and poet. In his 

 poem on " The Evolution of Plants," the series of changes in the 

 forms of the metamers is traced from the seedling, the process of 

 plant growth being used as an illustration of the general idea of evo- 

 lution from simple forms of life to more complex. 



Yet it appears very simple, when first we can see the new structure, 

 This in the world of the plants is ever the state of the child. 

 Growth is continued at once, one shoot coming forth from another, 

 Tvodes upon nodes towering up, all repeating the form of the first. 

 Still they are not quite the same; in manifold ways they are varied, 

 Each of the leaves, as you see, develops beyond the preceding. 

 Larger, and sharper in margin, as well as more deeply divided. 



Not only the differences of the vegetative internodes, but those of 

 the internodes that are modified as flower stalks and floral organs 

 were recognized, as well as the sexual differentiation of the stamens 

 and pistils, though the poem was published in 1700, three years before 

 the announcement of SprengeFs discovery of the fertilization of 

 flowers. Comparison of the series of gradually modified internodes 



"Other examples of anisophylly have been described by several botanical 

 writers. See Wiesner, ,T., Studien ueber die Anisophyllie tropischer Gewaeehse, 

 Sitzungsberichte der Matheniatisch-Natnrwissenschaftlichen Classe, Kaiserliche 

 Akademie der Wissenschaften. Vienna, vol. 10.3, 1894, p. 625. 



198 



