3. The Lesser Dodder (C. Epithymum).—A more slender plant, with thread-like stems, and flowers in small, compact, globular heads, with red calyx and cylindrical corolla. This species occurs principally on sunny heaths, where it is parasitic on shrubby plants, such as thyme and ling. It is much more common than the foregoing.
4. The Clover Dodder (C. Trifolii).—Very much like the Lesser Dodder, of which it is sometimes regarded as a variety. Its calyx is of a very pale colour, and is almost as long as the tube of the corolla, which is cylindrical in form. It is rare, but sometimes appears in undesirable numbers in clover fields.
All the species produce their flowers in August and September, but C. europæa may often be seen in bloom very early in July.
The seeds of the Dodder fall from the opened capsules during late summer and early autumn, alighting on the soil, or on the decomposing foliage that covers the ground, or on the rough barks of the tree that served as a host for the parasitic plant. The seeds of many other plants fall about the same time, but those of the Dodder do not begin to germinate until about a month later than the majority of these, in the following season, and consequently the young Dodder plants do not appear before their future hosts have had time to grow sufficiently large to support and nourish them. Perennial plants, too, which are attacked by the Dodder, have also produced strong shoots and leaves from their roots or underground stems by the time that the parasite begins its search for ready-made organic food; and it is clear that if the Dodder seeds germinated earlier in the season, the young plants would starve for want of suitable herbs to give them support and nourishment.
Greater Dodder, on Nettle--A Complete Plant.
When the seed germinates it sends out a filament which penetrates into the soil and fixes the seedling firmly. The other end grows upward, carrying up with it a little swollen mass of food-reserve, sufficient to support the growing seedling until it has had some chance of reaching a suitable host. The upper end of the seedling now sends out a filament which rapidly elongates, and, growing upward, searches for some stem on which to climb.
All this time the little mass of food-reserve is being rapidly exhausted, and if the young seedling fails to reach a suitable plant on which to climb it soon dies, for its lower extremity is unable to absorb sufficient food material from the soil; and the plant itself, having no chlorophyll, cannot decompose carbonic acid gas and build up organic material to add to its substance.
