. The anatomy of woody plants. Botany -- Anatomy. i8o THE ANATOMY OF WOODY PLANTS tissues are imagined to have been originally quite distinct from one another and to have been linked up by the formation of woody commissures organized entirely of secondary xylem and laid down by the activity of the so-called interfascicular cambium. The narrower and more depressed segments are supposed to owe their peculiarities to their late and entirely secondary origin. The five outstanding segments of wood in the oak and similar forms have been accordingly dubbed the fascicular wood, and the five intervenin
. The anatomy of woody plants. Botany -- Anatomy. i8o THE ANATOMY OF WOODY PLANTS tissues are imagined to have been originally quite distinct from one another and to have been linked up by the formation of woody commissures organized entirely of secondary xylem and laid down by the activity of the so-called interfascicular cambium. The narrower and more depressed segments are supposed to owe their peculiarities to their late and entirely secondary origin. The five outstanding segments of wood in the oak and similar forms have been accordingly dubbed the fascicular wood, and the five intervening de- pressed segments the interfascicular wood. An unfortunate situa- tion often encountered by this hypothesis is the fact that primary wood is frequently as well developed on the inner surface of the depressed segments as on that of the outstanding ones. The depression, as has been pointed out above, is susceptible of an entirely different explanation—namely, as the result of the local inhibiting influence of approximated broad rays on the rate of growth of the annual ring. In effect, moreover, the hypothesis of Sanio and Sachs derives woody from herbaceous forms, a conclusion entirely at variance with the paleontological his- tory of plants. It is clear that the woody forms have preceded herbaceous ones in all the main series of vascular plants. A single illustration will serve in the present connection. Our somewhat herbaceous existing lycopods and Equiseta are certainly known to have come from ancestral forms which possessed so conspicuously the arboreal and perennial habit that for many years a controversy raged as to their affinities. The majority of paleobotanists for a. FIG. 133.—Transverse section of a twig of the velvet oak (Qiiercus veliitina) showing five pairs of foliar Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not per
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