On the Origin of the Herbaceous Type in the 
Angiosperms. 1 
BY 
ARTHUR J. EAMES, A.M. 
Austin Teaching Fellow in Botany in Harvard University. 
With Plate XIV. 
I N those dicotyledonous stems where increase in thickness results in 
the formation of a solid woody cylinder, the latter has been 
considered to be the result of the fusion of a ring of separate fibro-vascular 
bundles by the extension of the fascicular cambium across the inter- 
vening tissue, and by the formation of xylem by this interfascicular cambium. 
Thus, apparently, the woody type of stem arises directly by the increased 
bonification and the enlargement of a stem which is, in its early structure, 
typically herbaceous. We may cite Sachs’ ‘ Lehrbuch der Botanik’, p. 131 
(1874), and Gray’s ‘Structural Botany ’, p. 73 (1879), as illustrating this 
method of development. This widely accepted view is evidently not the 
correct one, however. On the contrary, the herbaceous stem seems to be 
the higher type, and its separate bundles appear to have been derived from 
the woody cylinder by reduction, and by the dissection of the latter into a 
group of individual strands. In proof of this there is much evidence, both 
direct and indirect. 
Palaeontological evidence, in that no undoubted herbaceous fossil 
remains are known from the older periods, points to the modern develop- 
ment of this type. Further, the only surviving representatives of the 
arborescent Cryptogams which flourished in the Palaeozoic are herbaceous 
or semi-herbaceous in habit and structure. Their survival is probably due 
to an adjustment to modern conditions, this adjustment involving the loss 
of secondary growth, and the acquisition of a low or prostrate habit. 
Isoetes and Lycopodium may be compared with the ancient tree-like Lepi- 
dodendrids. As an herbaceous survivor of the arborescent Calamitean 
stock, Equisetum is another good illustration of the same principle. 
Secondary growth has practically disappeared and a stem structure simu- 
1 Contributions from the Phanerogamic Laboratories of Harvard University, No. 39. 
[Annals of Botany, Vol. XXV. No. XCVII. January, rgn.] 
