392 HARPER: FACTORS INFLUENCING DISTRIBUTION 
is “situated in a limestone formation.’ On investigation I find 
that this formation is lower Cretaceous. Professor W. L. Bray, of 
the University of Texas, to whom I wrote for further information 
about the range of 7: distichum in that state, informs me that it 
occurs on almost every stream in the Cretaceous area of Texas and 
probably on all on the Rio Grande Plain, also in all the bayou 
country of east Texas, north to the Indian Territory line. Dr. 
Havard, in his ‘‘Report on the Flora of Western and Southern 
Texas,” * mentions several stations for this species in the extreme 
southern part of the state. 
The southeastern limit of 7. distichum has been placed by Pro- 
fessor Sargent at Mosquito Inlet (about lat. 29°) on the east coast 
and at Cape Romano (about lat. 26°) on the west coast of Florida, 
but Dr. Small, who has recently been in southern Florida, tells me 
that it extends down the east coast to Miami (which is farther 
south than either locality mentioned by Professor Sargent) and is 
common in the Everglades near by. This is considerably beyond 
the known area of the Columbia formation, but still farther from 
the Lafayette. 
In Georgia, to which state my field work on this genus has 
been confined, I have seen 7. distichum on the Oconee River in 
Montgomery county, on the Ocmulgee in Dodge and Wilcox, on 
the Flint in Sumter, Dooly, Dougherty and Decatur, on the Och- 
locknee in Thomas, on the Chattahoochee River and Sowhatchee 
Creek in Early, on Lime Creek in Sumter and Gum Creek in 
Dooly, on Muckalee Creek in Lee and Kinchafoonee in Lee and 
Terrell, on Spring Creek in Decatur, Ichawaynochaway in Cal- 
houn and Chickasawhatchee in Dougherty; from all of which 
points the Lafayette formation is known or believed to be absent 
I have also observed this species in a few scattered localities away 
from the rivers in Sumter, Lee and Dougherty counties (from 
which localities the Lafayette may be inferred to be absent, though 
we have as yet no direct evidence that such is the case), and in 
lime-sinks near the Flint River in Dooly county. Other botanists 
have collected or observed it along the Savannah and Altamaha 
rivers ; and it doubtless extends from all the points just pa 
tioned down each river nearly or quite to its mouth. 
See 
* Proc. U. S. Nat. Mus. 8: 504. 28 S. 1885. 
