Physiological and Morphological Correlations in Herbaceous Angiosperms

Abstract

1. Herbaceous Dicotyledons have developed from arboreal dicotyledonous types by the formation of storage rays about the leaf traces. 2. In the more primitive herbs the foliar rays are shallow longitudinally, but of considerable radial depth. 3. In higher herbaceous Dicotyledons the foliar rays lose in radial dimensions as a result of the thinning of the woody cylinder, but this loss is largely compensated for by their increasing vertical extension, which often carries them through several internodes. 4. In the higher herbaceous Dicotyledons the foliar traces tend to multiply in number with the increased efficiency of the leaf. 5. Another important development in advanced dicotyledonous herbs is the progressive disappearance of cambial activity in the foliar trace, which often, in spite of this, is larger in size than the bundles of the stem. 6. The increase in number and importance of the foliar traces, as well as the greater relative importance of secondary axes in high herbs, leads to the crowding of strands at the node, which in turn results on the one hand in scattered distribution of the bundles in the stem, and on the other to formation of amphivasal strands. 7. The disappearance of secondary growth in foliar traces of advanced dicotyledonous herbs appears to be explainable on the grounds of physiological advantage. 8. Absence of secondary growth extends from the leaf traces to the rest of the bundles situated in the stem, and a condition practically monocotyledonous results.