Fig. 3. Iriartea ventricosa, a Bellied Palm (After Wallace). always has a straight trunk; the clambering species never have the trunk straight, and the full-grown coco palms have the trunk somewhat crooked. A singularity of the growth of palm trunks is that, with the exception of the 'bellied' trunks, they attain their full diameter while quite young—before, indeed, they set out to grow upwards. In other words, a palm grows endwise, as it were, but does not grow in diameter like the exogenous plants. It is therefore necessary that a palm should start on a broad base if it is to reach great height and great size. For this reason many of them when young look as if their fronds were growing from the top of a gigantic turnip-like stock. In some species as a trunk grows older it constantly strengthens its foundations by putting out rootlets just above the uppermost ones, very much like those starting from the lower joints of a cornstalk, and these roots continue to put forth until a compact and exceedingly tough support is built up about the trunk. In the paxiuba palm this buttress is one of the strange sights of the vegetable world. Fig. 4. Variations in the Form of the Trunk of Bocadja, Asuncion, Paraguay. Fig. 7 shows the remarkable rooting of the paxiuba (Iriartia exorrhiga). At the lower left side of the plate the details of one of these trunks are shown. These palms seem literally to be off the earth, for the trunk proper can scarcely be said to touch it. The figure in the upper left hand corner shows how the young paxiuba gets its start
Page:Popular Science Monthly Volume 60.djvu/398
POPULAR SCIENCE MONTHLY.