This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
In a paper (Russian) recently read before the Botanical Section of the St. Petersburg Natural History Society, Mr. K. Friderich describes in detail the anatomical structures to be met with in the aerial roots of Acanthorhiza aculeata, these roots presenting a remarkable example of roots being metamorphosed into spines. Supplementing this, E. Regel made the following remarks:
Palm trees, grown from seed, thicken their stems for a succession of years, like bulbs, only at the base. Many palms continue this primary growth (i.e., the growth they first started with) for fifty to sixty years before they form their trunk. During this time new roots are always being developed at the base of the stem, in whorls, and these always above the old roots. This even takes place in old specimens, especially in those planted in the open ground which have already formed a trunk, In such cases the cortex layer, where the roots break through, is sprung off. In conservatories, under the influence of the damp air, this root formation, on which indeed the further normal growth of the palm depends, takes place without any special assistance. When the palm is grown in a sitting room, one must surround the base of the trunk with moss, which is to be kept damp, in order to favor the development of the roots. When the base of the palm trunk has almost reached its normal thickness, then begins the upward development of the trunk, which takes place more slowly in those species whose leaves grow close together than in those whose leaves are further apart. In specimens of many species of Cocos and Syagrus, whose leaves are particularly far apart, the stems grow so quickly when planted in the open ground that they increase by five to six feet in height per annum. The stem of those palms which develop a terminal inflorescence have ended their apical growth by doing so, and wither gradually, In addition to this (withering) in the case, e.g. of Arenga saccharifera, new inflorescences are developed from the original axils (Blattachseln) from above downward, so that one sees at last the already leafless trunk still developing inflorescences in the direction toward the base of the trunk. Almost all palms with this latter kind of growth develop offshoots in their youth at the base of their trunks, which shoot up again into trunks after the death of the primary trunk, if they are not taken off before. As to the structure of the palm trunks out of unconnected wood bundles, the assertion has been made that the palm stem does not grow thicker in the course of time, and that this is the explanation of the columnar almost evenly thick trunk. But careful measurements that were made for years have led Regel to the conclusion that a thickening of the trunk actually takes place, which probably amounts to an increase of about a third over the original circumference of the trunk.