9o6 



THE NATURE BOOK 



the hot-house, yet the plant thriv^es 

 perfectly well. The great Aroids of the 

 genus Philodendron. and the strange 

 Monsteras, perch high in the branches 

 of trees, whence they send down long 

 aerial roots. Mthough a great deal of 

 moisture is absorbed from the air by 

 these processes, they not infrequently 

 find a final resting place in the damp 

 soil beneath. As is well known, a large 

 number of tropical Orchids are epiphy- 

 tical in habit, and by their gay flowers 

 adorn the branches of the forest trees 

 with lovehness. 



The plant is called upon to provide 

 accommodation for many of its own kind, 

 but it is to be feared that in a large number 

 of cases the guest is not a welcome visitor. 

 Quite often the host does not suffer 

 greatly from the attentions which are 

 pressed upon it. The mildly parasitic 

 Mistletoe does not appear to be a great 

 drain on the resources of the trees upon 

 which it grows. The plant selects a wide 

 range of hosts, embracing nearly all kinds 

 of the common deciduous trees. In 

 Britain, at any rate, the Mistletoe is chiefly 

 found on the Black Poplar. The manner 

 in which the parasite is cUstributed is very 

 interesting. In winter the white berries 

 are largely eaten by birds, and a certain 

 number of the seeds will be likely to 

 adhere to their beaks. To get rid of the 

 encumbrance, the bird cleans his bill by 

 rubbing it backwards and forwards on 

 the bark of a branch. In this way the 

 seed is placed in the best possible position 

 for its purpose. As the seed germinates, 

 roots are sent down into the tissue of the 

 branch on which it rests, and the Mistletoe 

 becomes quickly estabhshed. We may see 

 from the leaves of the plant that it is not 

 a very depraved parasite, the pale green 

 fohage indicating that the elaboration of 

 chlorophjdl is carried on to a certain extent. 



The story of the Dodder, a parasite of 

 the most abandoned description, is a 

 very different one from that f)f the Mistle- 

 toe. These remarkable plants, of which 

 there are several species found in Great 

 Britain, have given up all attempts to 

 make a hving for themselves in the 

 proper manner, and have appeared on 

 the scene as undisguised rf)bbers. The 

 life history of a typical species {Cuscuta 

 epithymum) is most curious. The seed 



of the plant germinates in the soil in the 

 usual manner of most plants. One fact 

 which is significant is that, unhke most 

 other flowering plants, the embryo of 

 the Dodder is not provided with any 

 reserve of food material. What little 

 nourishment the developing plant requires, 

 until it can enter upon its parasitical 

 career, is drawn from the albuminous 

 matter within itself. Soon after ger- 

 mination the thin radicle pushes its way 

 down into the soil ; meanwhile a red 

 filament spreads upwards. It is a matter 

 of urgency that the young Dodder should 

 at the earliest possible moment be able 

 to find a host, unless it is to perish 

 miserably. The red shoot elongates at 

 a considerable rate, and finally comes into 

 contact with a suitable plant. 



The particular species under con- 

 sideration is very partial to furze and 

 heather. At once the character of the 

 plant is revealed ; the root dries up, 

 the harmless-looking threads produce 

 suckers at the points of contact, and 

 entwine themselves round the stems of 

 the unfortunate plant selected as a victim. 

 From thenceforward the red shoots of the 

 Dodder increase at an incredible rate, 

 thrusting out in all directions, and, 

 wherever possible, affixing the suckers 

 which drain away the life from the 

 miserable host. About July, the Dodder 

 develops its clusters of small white flowers, 

 and soon afterwards the red filaments 

 decrease in the vigour of their growth, 

 and the parasite finally disappears. 

 Quite often the plant which has been 

 attacked is so miserably weakened that 

 it perishes before the Dodder ; but the 

 activities of the parasite are such that 

 it quickly transfers its operations to any 

 adjoining specimen which may be suitable 

 for its purpose. As showing what a 

 formidable enemy the Dodder may be to 

 the plant, e\'en the hardy furze bushes 

 not infrequently fall victims to the on- 

 slaughts of the parasite. 



Of root parasites there are two very 

 distinct groups — those which are only 

 partially dependent upon their hosts, 

 and those which can in no way support 

 a separate existence. The common wood- 

 land plant, the Cow Wheat (Melampyrtan), 

 attaches itself by discs to the surrounding 

 roots of its neighbours, yet this union 



