There is one thing, however, that the clover plant cannot do for the dodder, and that is, make its seeds. When the clover builds seeds, then they are clover seeds and will grow up as new clover plants. The dodder must build its own seeds if dodder plants are to grow from them. That is why we find growing out from the simple reduced thread of a stem, relatively large tufts of flowers (see fig. 106), which are very little different from usual flowers and which form seeds. The dodder belongs to the same family as the convolvulus, and though its flowers are small, if you examine them with a magnifying-glass you will see that they are very much the same in structure as those of the convolvulus.
When the young dodder plant grows out from the seed, it is a simple little thread with no leaves, and it keeps on growing at the tip, which it moves round till it feels some suitable host, then it quickly fastens on to it and lives on its food.
This is the general history of all kinds of parasites, for when any living thing ceases to use its structures and becomes a complete parasite it loses nearly all its parts, as there is no longer any need for them. So that parasites tend to sink to a lower level of development simply as a result of their way of living.
A plant which is largely a parasite, but yet does a little work for itself, is the mistletoe (see fig. 108). Its leaves are greenish, but not the true healthy green of a hard-working plant. If you can find a bough of mistletoe growing on an oak or apple tree, you will see that it has no root in the earth, but grows out of the bough of the host tree. It has sucker-like roots at the base of its stem, which go right into the stem-tissues of the host and get much nourishment from them.
Fig. 108. Young Mistletoe attached by its sucker-like roots S to a twig of apple A, split open.
In the winter, when the flow of food is very slow in the host, it is likely that the mistletoe does some of its own food building in its yellow-green leaves, which would be exposed to the full light, as the host’s leaves would have fallen away. The mistletoe has soft, white fruits which are scattered by birds, and as they are very sticky, they hold for some time on to the branch where they are dropped, and there the seedling sprouts and fastens itself on to the tissues of the host, growing every year with its growth.
