388 HarPER: FACTORS INFLUENCING DISTRIBUTION 
the U. S. Department of Agriculture,* although not regarding 
the two forms as specifically or even varietally distinct, has tabu- 
lated the results of many tests which show that the wood of the 
‘‘pond-cypress” is both heavier and stronger than that of the 
better-known plant. 
Turning now to ecological characters, the leaf-galls may be 
considered next. The leaves of both species are frequently more 
or less infested with galls, and as far as I have observed the galls 
on the two species appear to be different. Whether they are 
caused by the same or different insects I do not know ; this is a 
matter which deserves further investigation. 
In regard to habitat, it seems to be the prevailing opinion that 
T. distichum is confined to river swamps and 7. inéricarium to 
pine-barren ponds. This, however, is not always the case. The 
largest specimens of 7. imbricarium J have ever seen are in south- 
eastern Georgia, in deep-flowing water of creeks which never dry 
up, and yet they maintain their essential characters perfectly. Here 
the species is to all outward appearances growing under prac 
tically the same conditions which prevail in the rivers and creeks 
which 7. distichum inhabits. The habitat of the latter is also 
somewhat variable, including lime-sinks as well as river-swamps. 
Some say that 7: iméricarium grows in poorer soil, but this also 
is liable to many exceptions, to say nothing of the difficulty of 
defining accurately what constitutes a poor soil. 
In view of all these well-marked and constant differences, and 
others to be mentioned later, it seems to me that Taxodium dis- 
tichum and Taxodium imbricarium can no longer be consistently 
treated otherwise than as distinct species. They are certainly as 
distinct as Lycopodium lucidulum and L. porophilum, Juniperus 
Virginiana and J. Barbadensis, Pinus palustris and P. heterophylla, 
and a hundred others which might be mentioned. : 
During my investigations of the flora of Georgia in 1900, ide 
covered a most remarkable relation between the habitats of these 
two species of Zaxodium and the geological formations, 0” which 
I have based a new theory of their distribution. This theory 
has so far been fully substantiated by observed facts in almost 
every case, and the few apparent exceptions to it which have bee? 
* Cire. Div. Forestry, 19: 22. 1898. 
