172 CLIMBING PARASITES. GREEN-LEAVED PARASITES. TOOTH WORT. 



A comparatively large number of species, i.e. twenty-five, are distributed through 

 central and southern Europe. A few have been introduced recently for the first 

 time with seeds from the New World, as, for instance, C. corymbosa, which was 

 accidentally conveyed with lucerne seeds from South America to Belgium, and has 

 lattei-ly begun to range over central Europe. 



The various species of Guscuta attack chiefly small herbaceous, suftruticose, and 

 shrubby plants ; but a few American species coil themselves round branches growing 

 at the top of the highest trees. Notice has been especially drawn to certain 

 European species on account of their disastrous effects upon cultivated plants. The 

 most famous is Guscuta Trifolii, known as the Clover-Dodder, the appearance of 

 which in clover-fields causes so much anxiety to farmers, and which is so difficult 

 to exterminate. Another unwelcome visitor is Guscuta Epilinum, which coils 

 round flax stems and hinders their growth, and a third species, Guscuta Europoea, 

 sometimes ravages hop-plantations. This last is, indeed, the most widely dis- 

 tributed of all the Cuscutas, and extends from England over central Europe and 

 Asia to Japan, and southwards as far as Algiers. It is parasitic not only on hops, 

 but also on elder, ash, and various other shrubs and herbs; in particular it exhibits 

 a preference for nettles. 



The seeds of this species, and of Dodders in general, germinate on damp earth, 

 on wet foliage undergoing putrefaction, or on the weathered bark of old trunks. 

 The seedling, which in the seed lies imbedded in a cellular mass full of reserve- 

 food, is filiform and spirally coiled. It is twisted once, or once and a half, and 

 is thickened at one end like a club. In true Cuscutas, no trace of cotyledons 

 is to be perceived, nor does one find vessels in the interior of the seedling; but 

 chains of cells arranged with great regularity are noticed in the axis of the filiform 

 body, and are easily distinguished from the surrounding cells. In nature, the 

 seeds, after falling to the ground and lying there through the winter, do not 

 germinate till very late in the following year, i.e. at least a month later than the 

 majority of the other seeds reaching the same ground simultaneously with them. 

 Perennial herbs, also, have, by the time that germination takes place, already 

 developed shoots from their subterranean roots or rhizomes above the surface of 

 the ground, later a circumstance of great importance to the parasites. If a 

 Guscuta were to germinate early in the spring, it would not readily find close by a 

 support up which to twine; whereas later, there is seldom any lack of annual stems 

 or shoots of perennial plants in the immediate neighbourhood. 



When the twisted embryo germinates, it stretches and at the same time revolves 

 from right to left, assuming the shape of a screw and pushing its lower clavate 

 extremity out beyond the coat of the seed (see fig. 34^- '^' ^' *' ^' % This extremity forth- 

 with grows into the earth and fastens tightly on to particles of the soil, withered 

 foliage, and other objects of the sort. The other, attenuated extremity of the 

 filiform seedling, which is still wrapped in the seed-coat and the mass of reserve- 

 food, lifts itself up in the opposite direction, avoiding such solid bodies as it may 

 happen to encounter, and grows in a curve round them. Further growth does 



