176 DR. HARLEY ON THE PARASITISM OF THE MISTLETOE. 
Henslow*, Griffitht, Unger}, Schacht$, and Pitra| all agree, so far as their indi- 
vidual statements extend, in the following particulars :—The young plant first sends into 
the bark of the nourishing plant a single root, sucker, or senker, which, pressing inwards, 
comes into perpendicular relation to the wood of the nourishing plant, in the cambial 
layer of which the point rests, and there ceases to grow. In its passage towards the 
wood it gives off several horizontal or side roots, which run along the branch in the bark 
or upon the surface of the wood. These side roots give origin to perpendicular suckers 
(senker), which come into contact, like the original root, with the surface of the wood. 
“The wood and bark of the mother plant, in their periodical increase, form layers around 
the suckers, which grow in exactly the same manner in the cambial stratum" (Pitra, 
p. 61), and thus the hardened suckers come to be imbedded in the body of the wood. 
I will now proceed to detail the result of my own observation, introducing as occasion 
requires such particular statements of these several authors as are not mentioned here. 
First, as to the general characters and structure, and the arrangement and direction of 
that part of the Mistletoe which lies within the nourishing plant. | 
The base of the Mistletoe gradually diminishes in size from the surface of the support- 
ing branch inwards, that being the thickest part of the entire plant which corresponds in 
position to the outer surface of the last-formed layer of the wood. From this situation 
the base of the parasite, in its simplest condition, tapers as it passes towards the centre 
of the branch—gradually in the case of a young plant, so as to form a long tapering root 
(P1. XXVIII. figs. 1, 5c, &c.), suddenly in an old plant, forming a short, conical, woody 
plug, which, however, invariably ends in a slender cellular process (Pl. XXVIII. figs. 16, 
26,3a; Pl. XXIX. figs. 8, 10, & 11). 
But more commonly the base of the Mistletoe terminates in three or four, and some- 
times in five or six, such tapering roots. 
. When the base of the parasite does not exceed at its thickest part ths of an inch 
in diameter, itself and all its ramifications are composed of a delicate yellowish-green soft 
cellular tissue, which, shortly after making sections of a green branch charged with 
Mistletoe, shrinks below the level of the wood to the same extent as its younger layers of 
bark. When moistened, however, the young roots immediately swell up and project 
considerably above the surface of the wood. 
_ The young roots, and the equally soft cellular terminations of the older ones, are chiefly 
composed of delicate tubular cells, the 3}5th of an inch long and the z¢5oth of an inch 
wide, joined end to end, and arranged parallel to each other and to the long axis of the 
root (Pl. XXX. fig. 17 4). In cross sections of the root they have the appearance 
represented in figs. 14, 15. This parenchyma is pervaded by a few (the number depend- 
ing upon the age and size of the root) straggling plates of young prosenchyma, each 
composed of one or two layers of small thick-walled elongated cells destitute of markings. 
"*' Magazine of Natural History, vol. iv. p. 500, 1833. 
T On the Parasitism of Loranthus and Viscum, by W. Griffith, Esq. (Trans. Linn. Soc. vol. xviii. p. 78, 1841). 
+ Beiträge zur Kenntniss der parasitischen Pflanzen, Annalen des Wiener Museums der N aturgeschichte. Wien, 1840. 
§ Lehrbuch der Anatomie und Physiologie der Gewüchse, vol. ii. p. 465, 1860. 
|| Botanische Zeitung, von Hugo von Mohl, 1861. Leipzig, 4to, p. 61. 
