Field and Woodland Plants

by William S. Furneaux

Mistletoe.

There is no doubt but that the seeds of the Mistletoe are distributed from tree to tree by the agency of birds, especially the thrushes, which devour the berries in large numbers. The seed of the berry is protected by a covering which remains quite untouched by the digestive fluids of the bird, and consequently it is expelled intact with the excrement, and frequently drops to a branch of the tree, where it lodges in a crevice of the bark, and is securely fixed in its place by the slimy excrement in which it is embedded.

Here the seed germinates, sending out a little rootlet that always turns towards the bark on which it rests, and subsists for a time on the food-reserve that it contains. When the young root reaches the bark it becomes flattened against the surface, and spreads out, forming a disc that holds the seedling firmly to the tree.

A projection (the sinker) is then sent inwards from the disc, and this penetrates the bark, reaching the wood beneath, but does not enter the latter. This terminates the growth of the seedling for the first year, but as soon as the warm weather of the following spring commences, the sinker begins to spread over the surface of the outer ring of wood, while at the same time a new annual ring of wood begins to form outside, thus surrounding and banking in the sinker. It would appear, on making a section of the tree, as if the sinker had actually pushed its growth through the outer ring of wood, whereas it does not penetrate the wood at all, but is only banked up by the new wood that grows round it. This is repeated year by year, until the sinker is at last quite deeply set in the branch, being surrounded by the wood of several annual rings.

A Young Mistletoe Plant on the Branch of a Tree.
The Branch is Cut Longitudinally to Show the Suckers.

During the second year's growth the sinker sends out little roots which run up and down the stem, beneath the bark, and these give rise to new sinkers that grow down to the surface of the wood, and become, in turn, embedded in the new layers of wood that form round them. And while the young Mistletoe plant is thus securing a firm hold on its host, and withdrawing ready-made organic compounds from its sap, the outer green stem develops, and soon gives rise to the first pair of leaves.

If food is obtained in abundance, as is the case when the host is a tree of a soft and sappy nature, the growth is rather rapid; but otherwise the development is comparatively slow. In any case the age of the parasite may be ascertained by counting the number of annual rings of wood that lie outside the deepest sinker; and by this means it has been found that the Mistletoe may attain an age of over thirty years.

We have now to consider a group of plants, the parasitic habits of which would scarcely be suspected by an ordinary observer. They are green plants, with well-developed foliage leaves, and true roots which absorb mineral food from the soil. Their seedlings grow in the same way as those of non-parasitic species, deriving no nourishment from neighbouring plants, but obtaining all their food from the air and the soil, and building up all the organic compounds required for their growth by the agency of their own chlorophyll.

It is difficult to understand why these plants should afterwards produce suckers on their roots in order to obtain nourishment from other species, but they do this, and experiments have proved that the food thus obtained is more or less essential to their development. Some of them die while still young if grown apart from other species, and the others, under similar conditions, though they reach what we may term the adult stage, remain somewhat weak and stunted, and produce but few flowers and fruits.