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bibition there is no growth, and that, the more intense they are, the 
more rapidly the increase takes place—in other words, seemingly a 
very trivial result, the more water is supplied to a cell, other essen- 
tial conditions of course being alike, the larger will it grow. 
Now, if we agree upon this, in the case of Rhus, I think it is very 
natural to suppose, that the tissues on the supported side must be 
better supplied with water than the others. (I say with waver, not 
with nourishing sap, generally.) This more abundant supply of 
water would explain the greater activity of the cambium-cells in 
forming new cells, as their turgescence would be so much more in- 
tense, than on the opposite side, and it would also account for the 
extraordinary growth of the ducts by the increased facility for im- 
bibition, ; 
But where is that increased supply of water tocome from? Why, 
nothing. prevents the lateral rootlets from acting as water-carriers; 
they start from and are in close connection with the prosenchymatic 
wood-cells and the ducts, the very tissues whose principal function 
it is to convey the water to such places where it is needed. 
The only question is: Have those rootlets any. water to carry? 
or, Where do they receive it from? Ihave examined several hun- © 
dred plants of Rhus toxicodendron growing on trees. Of the first 
one hundred I kept accounts for the individual plants. An over- 
whelming majority of them grew on the east, north-east, north or 
north-west side of the trees. A remarkably interesting object is a 
long, old wall near the R. R. station, at Grinnell, on L. I., which 
runs from north to south. While on its east side the wall is so 
covered up by the most luxurious growth of Rhus, that hardly a 
brick can be seen; the west side can boast only of a very few strag- 
glers. Besides, I noticed very many plants that started ffom the 
ground, on the south side of trees. After a very short trip upward 
on that side, the stem would turn either west or east, and finally ran 
all the way up on the north side. 
Now it seems to be evident, that in these cases the stem wound 
its way to such places, where its rootlets could find most moisture in 
the cracks and recesses of the corky bark, and that is, of course, on 
the most shady side, the same that is so much preferred by crypto- 
gamic plants, which seem to know, too, that the atmospheric moisture 
is retained there longer and in greater quantity. ie 
I will just mention another observation bearing upon this point. 
In places where Rhus abounds, I found none growing on the smooth 
bark of beech-trees, while the oak, hickory and liquidambar of the 
same locality were well patronized. 
In conclusion, therefore, I venture to say: If we adopt the pres- 
ent theory referring to turgor and imbibition, and if it is true that 
the Poison Ivy thrives best in places where its lateral rootlets will 
find most moisture, ceteris paribus, we must suppose, that the excess 
of moisture supplied to the tissues of the supported side by the root- 
lets is the chief, if not the only, cause of the astonishing increase of 
the cells in number and size, and finally of the excentricity of the 
ith. ees! 
s _I have somewhat lengthily dwelt upon this subject, because some 
