118 
In Celastrus scandens, a woody twiner, the pith is always cen- 
tric, unless, by the growth of the supporting tree, pressure is made 
upon the inner side, when it becomes flattened. In other words, when 
the pith is eccentric, it is so from a mere mechanical impediment to 
the natural growth, which affects it in the same manner, and to the 
same extent, as it would any other plant, not aclimber. Mr, Ward’s 
examinations incidentally furnish the same results. For instance, 
' he says he always found the eccentricity less in specimens growing 
upon stones than in those upon trees. Now, when we consider the 
amount of heat absorbed by stones in the day-time, during the grow- 
_ ing season of plants, and that this is radiated during the night, it 
becomes evident that a plant growing in such a position, will be in 
a more equable temperature, and a higher one, than one climbing a 
tree trunk, It should, then, if Mr. Hyatt’s theory be true, show 
greater eccentricity of pith, whereas it shows less. 
One of the best marked specimens of eccentricity which I have 
was found on the north-west side of a tree trunk, near its base, 
where the sun could never reach it. 
The growth of plant stems generally does not depend upon the 
heat which they directly receive. The conditions necessary are 
sufficient nourishment at the roots and sufficient light and heat for 
the leaves to elaborate this food ; these conditions being present, the 
storing up of the products of vegetable digestion will go on in the 
stem. Gray says, “The greater the development of vigorous 
branches on a particular side of a tree, the more wood is formed, and 
the greater the thickness of the annual layers on that side of the 
trunk.” * 
These arguments seem to me sufficient to warrant the rejection 
of Mr. Hyatt’s theory. 
Whether the rootlets are, or are not, parasitic, as Mr. Ward in- 
clines to believe them, may now be considered. We have as nega- 
tive evidence against their parasitic nature, no recorded instance of 
their ever having been traced to the cambriun of a living support. 
‘On the other hand, in addition to the reasons which Mr. Ward gives 
for their being collectors of nourishment, either as parasitic or true 
roots, there is the fact that when climbing a support, the plant at- 
tains a much greater size than when unsupported. ‘This, at first 
sight, appears to be a good reason for thinking that the plant 
may receive other nourishment than that furnished by its roots 
that penetrate the earth. This, however, I hope to show, is only 
apparent, not real. But first let us grant, for the sake of argument, 
that these rootlets do collect nourishment. Then they cannot ac- 
complish this in a parasitic way, because the plant will grow as high, 
as large, and spread as extensively upon a dead tree as upon a liv- 
ing one. This could ngt occur if the plant were, in any degree, 
parasitic. So, then, if the rootlets do collect nourishment they must 
do so in the character of true roots. Let us see where such an 
hypothesis would lead. It would inevitably bring us to the con- 
clusion that Rhus toxicodendron puts forth true roots in the great- 
* Structural and Systematic Botany. Note on page 130. 
