^' 5. Adamson. NOTE ON THE ROOTS OF TERMINALIA BY R. S. ADAMSON. [TEXT-FIGS. 3-7.]

Size: px

Start display at page:

Download "^' 5. Adamson. NOTE ON THE ROOTS OF TERMINALIA BY R. S. ADAMSON. [TEXT-FIGS. 3-7.]"

Ursula Peters
5 years ago
Views:

1 ^' 5. Adamson. NOTE ON THE ROOTS OF TERMINALIA ARJUNA, BEDD. BY R. S. ADAMSON. [TEXT-FIGS. 3-7.] The material examined was collected by Mr. I. H. Burkill, near Sembadow, in the Satpura Hills of Central India, from the banks of the Sipra River, and sent by him to Professor Seward, who handed over to me for investigation. Terminalia Arjuna Beddome is a large tree belonging to the natural order Combretaceae,' and growing to a height of sixty to eighty feet. The species is confined to India and Ceylon, where it occurs commonly along the banks of streams and rivers.^ From the trees growing on the banks of a river, certain roots grow out horizontally into the river bed, among the stones, or just below the surface of the water. From these roots lateral branches are given off that rise vertically to the surface of the water or mud. It is such roots that I have investigated. The rivers in the district from which the material was obtained dry up during the hot season, when they are represented by a series of pools. The material was collected in October, 1908, when the level of the river was beginning to fall, and beneath all the trees of Terminalia Arjuna was a thick growth of the small apogeotropic roots among the stones and mud of the river bed. In some of the deeper pools, as Mr. Burkill states in a letter, the horizontal roots bend up till they reach the surface of the water, where vertical- roots are produced; they afterwards bend down again. STRUCTURB OF THE HORIZONTAL ROOTS. The roots seem to be primarily triarch, though other primary strands appear later, so that older roots are hexarch to octarch. Large vessels are produced in the secondary wood, but do not occur in that formed previous to the activity of the cambium. The medullary rays consist of a single row of cells, or are rarely two to three rows of cells in breadth ; they broaden out slightly in the phloem, owing to the greater breadth of the cells in that region. The phloem consists of three kinds of cells: (i.) sievetubes and companion cells, (ii.) large numbers of parenchyma cells < Hooker, J. D. Flora of British India. ' Brandis, D. Indian Trees, 1906.

2 Roots of Terminalia Arjuna yrhich often contain stellate groups of crystals of calcium oxalate, and (iii.) occasional fibres, either singly or in groups. The pericycle is not lignifled, and the endodermis is a well-marked layer, vvith both radial and inner walls somewhat thickened; occasional passage cells occur. The cortical tissue is very loose with large lacunae (Fig. 3). The individual cells are cylindric and arranged ifi irregularly radial rows. Beneath the epidermal layer is a hypoderm of elongated cells, polygonal in cross section, whose walls are slightly thickened. _. CoKtex Fig. 3. Transverse section of cortical part of root. Very soon after the beginning of secondary thickening a periderm is formed in the outer layer of the pericycle; the primary cortex is afterwards cut off. An aerating tissue forming a ' secondary cortex" is then formed internal to the periderm. This is mainly derived from the secondary phloem' (Fig. 4). The cells of the phloem parenchyma split apart from one another, but also conjugating parenchyma is formed. In addition, some cells forming Cf. Schenk, H. Flora, 1889.

3 R. S. A damson. a phelloderm, are cut off internally by the phellogen, and add to this tissue. Crystals of calcium oxalate occur in some of the cortical cells, especially in the inner ones (Fig. 4). Cortex- - Periderm. _... Lacuna. Pig. 4. Transverse section of root, showing lacunae in secondary phloem. STRUCTURE OF THE VERTICAL ROOTS. In general structure these are very like the horizontal roots, hut on a smaller scale. They differ from ordinary pneumatophores' in heinj* freely branched, the branches arising endogenously in the normal manner; like the horizontal roots they are at first triarch, with additional protoxylem groups appearing later. Near the apices of these roots the cortex is simple with a few < Karsten. Uibliotheca Botiinica, XXII., 1891.

4 Roots of Terminalia Arjuna. 153 large intercellular spaces. As the root increases in size the cortical cells grow irregularly, the result being that the cells separate from one another, but in places remain attached by lateral processes. A large lacunar system is thus formed. The connecting processes are at flrst produced mainly on the radial walls of the cells and to a less extent on the tangential walls, so that the cells come to be arranged in radial chains (Pig. 5). In time the processes are cut off by transverse walls. This method of growth of a lacunar system has been termed by Karsten'" conjugating parenchyma."' The process is helped by the rows of cells simply splitting away from one another. A point in which the roots differ from typical pneumatophores* Fig. 5. Longitudinal section of cortex of a young root, showing beginning of " conjugating parenchyma." is that the root-tip is covered by a deflnite root-cap, though this cap is not of the normal structure seen in terrestrial roots.' It extends much further back than usual; the cap-cells continue as a lhniting layer two to three cells deep over the region normally occupied by the root-hairs and do not finally disappear till a considerable distance behind the apex, at a point where the tissues > Solereder, Syst. Anat. Dikot, 1908.» Westermaier. Zur. Kenntniss der Pneumatophoren, * Jiincsewski. Ann. Sci. Nat., 1874.

5 154 R. S. Adamson. are fully differentiated. In structure the root-cap is also remarkable i(fig. 6); it is of considerable thickness, from twenty to twentyfive layers of cells being present in some cases above the apex. A: B Pig. 6. Longitudinal median section of young root cap. f Pig. 7., Transverse section tbroughroot cap, along Une A-B, in Fig. 6. Tbe tissue forming tbe cap appears to be differentiated into two parts, a central portion over tbe growing-point of tbe root (Fig. 7) and a peripberal portion (see Figs. 6 & 7). Tbese regions are

6 Roots 0/Terminalia Arjuna. 155 distinguished partly by the form of the cells, but more distinctly by their contents. The central core consists of large cells which are square in longitudinal section, while the others are elongated in the axial direction; intermediate stages however occur. The differentiation of contents is very sharp; the cells of the central core contain clear vacuolated protoplasm with prominent nuclei while the surrounding cells have small inconspicuous nuclei and are filled with a deeply-staining granular substance. No intercellular spaces occur between the cells of the root-cap. Root-caps of this form were found both in the horizontal and the vertical roots; in neither cs^se are root-hairs developed at all. Slight structural differences were noticed in.roots collected from different environmental conditions: those growing wholly or partially submerged have the vascular, tissues less developed, and do not form a peciderm till.a later period.; also the hypodermal layer is less distinct, especially in the vertical roots whicji are less branched or unbranched. In some roots from the edge of the river, which presumably had been dry for a longer period, the conjugating parenchyma is much less developed. Some seedlings were also examined; these did not show any trace of the peculiar roots,'but since the seeds germinate and start life on the dry banks and not in the river-bed, this is not so remarkable. In general structure the roots of these seedlings are very like those described, but without the great cortical lacunar system. The roots of Terminalia differ markedly from the pneumatophores of Sonneratia,^ in not possessing the striking peripheral layer of cork with lenticels characteristic of the latter genus. Even old roots of Terminalia which had cast off the primary cortex had no lenticels. The hypodermal layer of cells in Terminalia is not connected with a cambial layer, and no openings communicating with the outside air occur in it. Another point in which roots of Terminalia A rjuna differ from typical pneumatophores is the complete absence of stem characters, such as pith, etc.; as far as vascular anatomy goes they are perfectly normal roots. Though these roots seem to be for purposes of aeration, they cannot be described as as true pneumatophores, in Westermaier's sense.* Mr. Burkill suggested from observations made while collecting the material that the aerating roots of Terminalia are probably ' Goebel. Ber. Deut. Bot. Ges., 1886.» We8terfnaier. Loc. cit., 190Q,

7 156 Roots of Terminalia Arjuna. ephemeral, and functional during the wet season only. He considers it as probable that they die off when the rivers run dry. This suggestion appears quite plausible, since, when the soil is dry, the perennial horizontal roots would be in a medium where ordinary respiration is possible. This is a point that can only be settled by further observations of the plants in their native habitat. SUMMARY. The vertical roots are for purposes of aeration as shown by the great development of the lacunar system. The lacunx in the primary cortex are developed mainly from conjugating parenchyma. A secondary aerating cortex is produced in old roots in the region of the secondary phloem. No root-hairs are present, but a root-cap of a peculiar nature is formed. No direct connexion with the outside air was noted. These roots have none of the stem characters of typical Mangrove pneumatophores.

Visit For All NCERT solutions, CBSE sample papers, Question papers, Notes for Class 6 to 12. Chapter-6 ANATOMY OF FLOWERING PLANTS

Visit For All NCERT solutions, CBSE sample papers, Question papers, Notes for Class 6 to 12. Chapter-6 ANATOMY OF FLOWERING PLANTS Chapter-6 ANATOMY OF FLOWERING PLANTS POINTS TO REMEMBER Anatomy : Anatomy is the study of internal structure of organisms. Plant anatomy includes organisation and structure of tissues. Tissue : A group