386 HARPER: FACTORS INFLUENCING DISTRIBUTION 
of the leaves likewise into a horizontal position. In 7. zmbricarium, 
on the other hand, the leaves are normally more or less appressed 
to the branchlets, which have lost their dorsiventral character. 
The branchlets have been described by Professor Sargent and 
others as ‘erect or pendulous,” and from a herbarium specimen 
it would usually be impossible to ascertain which of these two 
positions they had assumed in life. But they would be much 
more correctly described as normally erect, occasionally somewhat 
spreading, very rarely (never in perfect specimens) drooping. It 
is interesting to note that the leaves and branchlets of the two 
species of the allied genus Segwoia differ in much the same way. 
I have not noticed any difference between the fruits of the two 
species, but Nuttall says of 7. iméricarium “nuts larger,” and 
Endlicher * probably following Nuttall, says of 7. ascendens 
Brong., ‘“seminibusque majoribus.”’ a 
The difference in size, mentioned by some authors, does not 
appear to be constant, as remarked by Croom. In Georgia, 
where both species are abundant, 7. imbricarium often attains as 
largea size as T. distichum, but the former probably begins to fruit 
at a smaller size (though perhaps not at an earlier age, as it is said 
to be of slower growth). 
One characteristic difference, which does not seem to have 
been noted before, is found in the enlargement at the base of the 
trunk, which is usually more abrupt in 7. zmbricarium than in TZ. 
distichum. In Coffee county, Georgia, I have walked entirely 
around a specimen of 7, imbricarium on its enlarged base, 4 feat 
which would be impossible with any specimen of 7. distichum \ 
have ever seen. Furthermore, the enlargement of the trunk of 7. 
distichum is approximately conical, with its’ greatest slope at or 
below the surface of the ground (or water, as the case may be), 
while that of 7. imbricarium is conoidal, with its greatest slope 
some distance (a few inches to a foot or two) above the ground. 
In the many thousands of individuals of 7. imbricarium which I 
have seen I have never observed any deviation from this char- 
acter. The longitudinal ridges traversing this enlargement 4f° 
usually quite sharp and prominent in 7. distichum, and rounded 
ee 
* Syn. Con. 69. 1847. 
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