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est possible profusion in those situations where there is: the least 
possible nourishment. In other words, it would require us to be- 
lieve that this plant has the laws that generally govern root- 
growth reversed in its favor. NowI have repeatedly observed that 
this plant, lying prostrate upon the ground, roots in just about the 
same manner, and to the same extent, as any other ordinary plant 
would root under the same circumstances. Stems growing in such 
situations, have their pith centric. A large number of plant stems 
will strike true roots freely in the presence of moisture, and, when 
surrounded by proper nourishment, these roots will increase exten- 
sively. Rhus toxicodendron being no exceptive to this rule, can it 
be believed that it will, in the absence of these conditions, root a 
hundred times more freely? Ihave no hesitation in rejecting a 
theory which demands such credulity. 
If, then, these rootlets do not collect nourishment in any manner— 
and, if my reasoning be correct, they do not—any theory to account 
' for the eccentricity of pith, founded upon such office, necessarily 
' falls to the ground. How, then, shall we account for it? I think. 
we shall arrive at a solution of that question when we have solved 
one which should have preceded it, and that is in response to what 
stimulus do these innumerable rootlets issue ? 
Dr. Bigelow in his “ Medical Botany,” published in 1820, says he 
has “observed that young plants of Rhus radicans frequently do — 
not put out rooting fibres until they are several years old, and that 
they seem, in this respect, to be considerably influenced by conti. 
guity of supporting objects.” Mr. Ward mentioned a “vine up- 
wards of an inch in diameter at the base” which “had climbed a 
cedar tree to the top, and, no longer finding anything to adhere 
to, sent out free fruiting branches nearly half an inch thick.” Later 
on he says, “ On the projecting branches of the same vine, bearing 
the berries and showing no tendency to cling, there was no appreci- 
able eccentricity.” Here we have at the top of a tree which the 
plant bad climbed, free branches half an inch thick without rootlets, 
This goes to confirm Dr. Bigelow’s remark concerning the influence 
of contiguity of supporting objects. I have made numerous obser- 
vations upon this point, and all tending to establish the principle 
that contiguity of supporting objects is the main factor in the cau- 
sation of the emission of rootlets. One instance only will I mention 
particularly. A vine about an inch in diameter had climbed the 
perpendicular face of a large rock, on its north side, adhering very 
closely. At the top it branched extensively, some of the branches 
* being nearly half an inch in diameter, and, ascending from the rock, 
looked very much like a bush growing there. All of these ascend- 
ing branches, even tothe largest, were very nearly free from rootlets. 
In cases where the stem had at any previous time adhered, and the 
- union had been broken, I noted both a tendency toward recovery 
from eccentricity of pith, and a marked diminution in the produe- 
tion of rootlets as compared with those adhering portions of the 
stem both above and below. These facts, to my mind, demonstrate 
conclusively that Rhus toxicodendron is stimulated to put forth 
rootlets for climbing, by contact with a supporting object, in just 
