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Volume 31, 1898
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Second Meeting : 14th June, 1898.

Dr. T. M. Hocken in the chair.

New Member.—Professor W. Blaxland Benham, D.Sc.

Paper.—“On some Peculiar Attachment-discs developed in some Species of Loranthus,” by G. M. Thomson, F.L.S.

Abstract

The author described the various forms of parasitic flowering-plants which were to be found in New Zealand, dwelling especially on the dodders (Cuscuta) and the various species of mistletoe (Loranthus, Tupeia and Viscum). The dodders belong to the Convolvulus family. The seed falls into the ground and germinates there in the usual manner, putting out a delicate thread-like shoot. When this comes in contact with any part of a neighbouring plant it at once coils itself round it, and developes wart-like suckers, by means of which it abstracts nourishment from its host. These suckers send out minute root-like processes, which penetrate the tissues of the host, but this penetration, as a rule, does not extend much deeper than the cortex, so that the material abstracted consists of the already assimilated juices of the plant, and the parasite is therefore spared the necessity of producing leaves. As soon as the suckers develope the primary root dies. The mature dodder is then

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a leafless parasite, consisting of thin reddish thread-like stems with pretty little pink flowers.

The seeds of mistletoe, on the other hand, are quite incapable of growing in the soil. They are eaten by birds, and pass undigested through their alimentary canal. If they are dropped on a tree they germinate in due course, and the radicle attaches itself to the bark like a little cushion, from the centre of which a conical mass of cells penetrates the tissues of the host as far as the wood-cells. Round this central cone the host-plant each year builds a rampart of new wood-cells, so that the mistletoe becomes, as it were, naturally grafted into the host. Its sucker, being in contact with the core of the plant, absorbs the unassimilated sap of the latter, and therefore the mistletoe has to do its own, digestive work, and developes green leaves for the purpose.

The specimens referred to in the paper belonged to the yellow mistletoe (Loranthus flavidus), and were parasitic on the white birch (Fagus solandri); they were found at Lake Wakatipu by Miss Marchant. The mistletoe, instead of having one point of attachment, as is commonly supposed to be the case, was attached along the stem of the host-plant like a large dodder by means of numerous cushion-like discs, but these sent no suckers through the bark, and seemed to serve mainly as clasping organs. A somewhat similar instance is described and figured by Chatin (“Anatomie Comparée des Vegetaux”), of a species of Brazilian Loranthus parasitio on a Citrus, but in this case the clasping discs developed piercing suckers.

Specimens of Loranthus and Tupeia from the Town Belt were also exhibited.