//). 
Vol. VI., No. 23.] BULLETIN oF THE ToRREY Botanica Cius. [New York, Nov., 1876. 
§ 126. The Eccentricity of the Pith of Rhus toxicodendron.— 
This subject was briefly discussed at the April meeting of the Club, 
by Mr. J. B. Hyatt, who seems to have been the first to notice the 
fact. (Butuerry, Vol. VL, p. 47.) An article on the subject, written 
by Lester F, Ward, had appeared in Zhe American Naturalist, for 
that month. 
Mr. Hyatt attributes this eccentricity to the heat which the Rhus 
receives from its support on the inner, or supported side. 
Mr. Ward leaves the question somewhat open, though he inti- 
mates quite strongly his conviction, that it is due to absorbtion of 
nourishment by the aerial rootlets; that these rootlets are parasitic, 
and that they deposit the nourishment, which they collect near the 
point of their emission from the stem. At least, after detailing his 
numerous examinations of different specimens of the plant under 
widely varying circumstances, he says, “these facts all unite in 
pointing to a physical connection of some kind between the pene- 
tration of the rootlets and the eccentricity of the pith. The notion 
thus far entertained, and which has found its way into our standard 
text-books, that these rootlets are not for absorbing nourishment, 
but for climbing, may, in future, require some modification.” An- 
ticipating the objection that these rootlets are neither parasitic, nor 
merely for climbing, but true roots, finding “congenial soil in the 
corky layer of bark, in the soft mass of decomposed wood, and even 
to somé extent in the minute cryptogamic vegetation that always 
exists among them, even when clinging to walls of brick or stone,” 
he is at a loss how to account for “the strange eccentricity of the 
annual rings ” Se : 
Neither of the foregoing explanations is satisfactory to my mind, 
That of Mr. Hyatt is exceedingly unsatisfactory, because, if true, all 
climbing plants closely fixed to supports larger than themselves, 
should show the same eccentricity to a greater or less extent, directly 
in proportion to the heat absorbing power of such support. Facts, 
however, are not in harmony with any such conclusion. I have ex- 
amined .a number of climbing plants with reference to this point 
with a negative result in every case. ‘ : 
Eccentricity of pith I found in Rhus toxicodendron, Ampelopsis 
quinguefolia, and, in the only specimen examined, Hedera Helix 
(English Ivy), but in neither of these have I been able to trace any 
apparent connection between the degree of eccentricity, and the 
amount of heat which the plant received from its support. In Am- 
pelopsis quinquefolia the eccentricity seems quite variable, being 
sometimes on the inner, sometimes on the outer side. In the great- 
er number of instances, however, the thickest growth was on the 
unsupported side, or exactly the reverse of the condition found in 
Rhus toxicodendron. In the single case of Hedera Helix examined, 
the thickest growth was on the supported side. The plant was 
growing up the north face of a ledge of rocks, where the rays of the 
sun could never reach it. This, it will be remembered, is a root 
climber. 
