File:Plants of New Zealand (1906) (14784227555).jpg

Identifier: plantsofnewzeala1906lain (find matches)
Title: Plants of New Zealand
Year: 1906 (1900s)
Authors: Laing, R. M. (Robert Malcolm), b. 1865 Blackwell, E. W. (Ellen W.)
Subjects: Plants
Publisher: Christchurch : Whitcombe and Tombs, Ltd.
Contributing Library: The LuEsther T Mertz Library, the New York Botanical Garden
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden

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the embryo, but from the stemof the plant—so, on account of their mode of origin, they aretermed adventitious roots, i.e., roots not formed in the naturalmanner. They are obviously used to stay the plant, and giveit foothold in the soft mud. Avicennia has few of thesesupports, but makes use of its roots in a way that is almostunique. Kirk (Forest Flora, p. 272) tells us that, At lowwater their naked trunks are exposed, and the mud is seen tobe thickly studded with erect shoots from 1 ft. to 3 ft. high,,given off from the tangled roots. He has here fallen intoerror. The structures described are not shoots, but upwardgrowing roots containing chlorophyll, and are not more than afoot in height. They never produce leaves, and only veryrarely fork or branch. They must therefore be regarded as.roots which have lost their most characteristic reaction, andwhich grow upwards instead of downwards. As they containchlorophyll, it is probable that they assist in the work of THE VEEBENA FAMILY 357
Text Appearing After Image:
Fig. 117. Mangrove roots. 358 PLANTS OF NEW ZEALAND nourishment. But they have a more remarkable functionthan this. If they are closely examined, they will be found tobe studded with pores, similar to the lenticels found in thebranches of many trees. These pores are for the purpose ofallowing air to enter and leave the internal tissues of theplant. The mangrove, growing in the tidal mud, wiiere littleor no oxygen can get to the roots directly, turns the tips ofits roots into the air, and by this ingenious means obtains itsnecessary supply of oxygen. Nor is this the only adaptationof the root to its altered environment. Most rootlets areprovided with a small shield at the tip, technically known asthe root-cap. This protects the tender, growing point as itforces its way between the particles of the soil. Such protec-tion would be superfluous in plants rooting in water,—in themangrove, and in many marsh-growing plants, it is wanting. But the grey-green, asparagus-like pegs which arise

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