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XI. On the Parasitism of the Mistletoe (Viscum album). By Joun HARLEY, M.D., 
JM.E.C.P., &c. Communicated by J. D. HOOKER, M.D., F R.S., F.L.S. 
(Plates XXVIIL, XXIX., XXX.) 
Read March 5th, 1863. 
SOME three years ago I turned my attention to small Vegetable Parasites, hoping that 
they would throw some light on the cause of cancer and analogous diseases in the human 
subject, or that, at least, they would direct my investigations into the nature of these 
obscure growths. But on referring to the literature of our great vegetable parasite, the 
Mistletoe, I was surprised to find that, although the strueture and development of the 
wood, the ovules, and the pollen of this plant, and the anatomy and germination of its 
seed, have been very fully and carefully investigated*, our knowledge of the anatomical 
and physiological relations of the parasite to the plants upon which it grows was still 
imperfect. The observations of our own authors in particular are most fragmentary and 
superficial; and the English student, if he wanted definite information respecting the 
nature of the parasitism of the Mistletoe, would seek in vain for that information in our 
own language; and, what is still more remarkable, the subject has never been illustrated 
by our own botanists. Our fellow-labourers in Germany have, however, advanced our 
knowledge of the subject very considerably, but yet their observations are incomplete 
and sometimes contradictory; and as I have found them in some essential particulars 
at variance with my own observations, I have thought it desirable that a subject so 
important to vegetable physiology as the nature of the parasitism of the Mistletoe should 
be more fully considered. The present paper professes to be an investigation into the 
anatomical relations of the Mistletoe to the plants upon which it grows, and a deduction 
therefrom of the general physiological relations existing between them. 
The Mistletoe attaches itself to the nourishing plants by roots, some of which are 
horizontal and confined to the bark, the others are contained within the wood. 
* Decaisne, M. : Mémoire sur le Développement du Pollen, de l'Ovule, et sur la Structure des Tiges du Shi (Acad. 
Roy. Bruxelles, 1839, vol. xiii). Développement du Pollen dans le Gui (Académie des Sciences, vol. viii. p. 201). 
De la Structure ligneuse du Gui (Comptes Rendus, 1839, p. 204). 
Kieser: Mém. sur l'Organisation des Plantes, 1814, p. 305, tab. 22. 
Bischoff: Lehrbuch, vol. ii. p. 62. io d 
Link, H. F.: Icones selecte Anat. Bot. 1842, fascie. iv. tab. 8, all the seven figs. leones Anat. Bot, fascie. ii. 
tab. x. 7, 8. 
Richard: in Jussieu's Mémoire (Ann. Mus. vol. xii.). 1 wee 
Griffith, W.: On the Development of the Ovules of Loranthus and Viscum (Trans. Linn. Soc. vol. xviii, ). 
Loudon, J. C.: On the Germination of Viseum album (Arboretum et Fruticetum, vol. i. p. ges " 
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