212 MISTLETOES AND LORANTHUSES. 



is, presently, solid resisting wood. The root being no longer able to split the tissue 

 with its point, is stopped in its growth at this spot. But there is nothing to pre- 

 vent its continuing to grow along a course somewhat nearer the periphery, and 

 outside the limit of the new annual ring of solid wood, where a fresh development 

 of soft and tender cells has taken place in the cambium, and this indeed actually 

 happens. 



Thus, every addition to the length of the Loranthus-root, as it grows onward 

 between the wood and the cortex of the oak -branch, is further removed from the 

 axis of the branch; or, in other words, the surface of contact between root and 

 wood has the conformation of a flight of stairs, of which the lowest step constitutes 

 the base, and the uppermost the apex of the root (see fig. 48^). These steps are 

 very small, their height varying from about 5 mm. to 7 mm., but they may be 

 distinguished quite clearly in longitudinal sections, on account of the darker colour 

 of these roots contrasting with the lighter oak-wood. Nutritive fluids are imbibed 

 by the Loranthus-root from the wood of the oak at the surface of contact, and it 

 is probable that this absorption takes place especially at the notches forming the 

 steps. The root can only elongate, naturally, during the period when there is a 

 young and fi-agile cell-layer suj^erimposed upon the solid wood, whence it follows 

 that in Loranthus the continuation of the root's growth is more dependent upon a 

 particular season and upon the annual progress of development of the host than is 

 the ease with the Mistletoe. There may be some connection between this circum- 

 stance and the fact that the Mistletoe possesses evergreen leaves, whilst Loranthus 

 is green only in summer, acquiring fresh green foliage in the spring in the very 

 same week as the oak does, and casting its leaves in the autumn simultaneously 

 with the tree it infests. 



The stem which issues from the embryo of a Loranthus-seed grows away from 

 the oak-branch into the open air, and develops with great rapidity at the expense 

 of the nutriment absorbed from the host's wood, and conveyed to it by the root 

 above described, into a dense, dichotomouslj^-branched bush. In summer it is not 

 unlike a Mistletoe-bush, but in autumn, when it has cast its leaves, it acquires a 

 totally different aspect owing to the dark-brown branches and the conspicuous 

 yellow clusters of berries. 



Bushes of Loranthus grow to a greater size even than those of the Mistletoe; 

 their stems attain not infrequently a thickness of 4 cm., and clothe themselves with 

 a blackish, rugged bark, the older stems of this kind being then usually studded by 

 an abundance of lichens. At the spots where stems of Loranthus spring from an 

 oak-branch they are always surrounded by a great rampart of wood belonging to 

 the oak, and the base of the stem is often fixed in a deep symmetrically-rounded 

 bowl reminding one vividly of the similar structures out of which the stems of 

 Balanophorese arise. But whereas in Balanophoreae this bowl-shaped rampart 

 appertains to the parasite, in Loranthus it is formed from the wood of the host- 

 plant, i.e. the oak. It must, in the case we are considering, be interpreted as an 

 exuberant growth of wood-cells and compared to the hypertrophies called galls. 



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