The Encyclopaedia Britannica; .. A dictionary of arts, sciences and general literature . pally by additions totheir extremities, which are constantly renewed, so thatthe minute fibrils serve only a temporary purpose, andrepresent deciduous leaves; but in large trees which formthick roota an increase in diameter occurs in the rooteimilar to what is seen in the stem itself. In some plantsno roots are formed at all, thus in the Orchidaceous plants Epipogium Graelini and Corallorhiza innata, and also inLemna arrhiza, no roots occur. Roota may be given offfrom any portion of a stem, originating as
The Encyclopaedia Britannica; .. A dictionary of arts, sciences and general literature . pally by additions totheir extremities, which are constantly renewed, so thatthe minute fibrils serve only a temporary purpose, andrepresent deciduous leaves; but in large trees which formthick roota an increase in diameter occurs in the rooteimilar to what is seen in the stem itself. In some plantsno roots are formed at all, thus in the Orchidaceous plants Epipogium Graelini and Corallorhiza innata, and also inLemna arrhiza, no roots occur. Roota may be given offfrom any portion of a stem, originating as cellular prolonga-tions from the inner portion of the stem, and coming oflf atany point of the stem, or at small lenticular points to whichthe name of leniicels has been given by some. When thestem is more or less horizontal the roota given off from itpass directly into the soil; but if the stem be erect theypass for a certain distance downwards through the air,and are called aerial. The latter are well seen in the Screw-pine (Pandanus), the Banyan (Ficus indica, fig. 59), and m^s^^^. Fig. 59. Ficut indica^ the Banyan tree, sending out numerous aerial roots, which reach the soil, and prop the brancuea. many other species of Ficus, where they assist in support-ing the stem and branches. In the Mangrove they oftenform the entire support of the stem, which has decayedat its lower part. In Tree-ferns they form a dense coatingaround, and completely concealing, the stem; such is alsothe case in some Dracaenas and Palms. In Epiphytes, orplants growing in the air, attached to the trunks of trees,such as Orchids of warm climates, the aerial roots produceddo not reach the soil; they continue always aerial andgreenish, and they possess stomata. Delicate hairs areoften seen on these epiphytal roots, as well as a peculiarinvestment formed by the cells of the epidermis which havelost their succulent contents and are now filled with layer is called velamen radicum, or covering of the
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectencyclo, bookyear1902
