First, Texas was not admitted by virtue of a treaty. The Senate rejected one in 1844, partly because Texas was a slave state.
Texas entered the Union by way of a congressional resolution in 1845 that required only a majority vote in Congress rather than two-thirds approval in the Senate for a treaty. One term of the resolution was that Texas could divide itself into four more states. There was nothing about any right to secede.
Remember, when Texasn voted on Feb 23, 1861, to secede, the result was a war. If Texas had a legal right to secede, there would have been no war."
Damon Ball, who wrote this explanation which appeared in the San Antonilo Express News Letters to the Editor Section about three months ago, suggested that our Gov. Perry should read T.R. Fehrenbach's classic history of Texas, "Lone Star," specifically Pages 263-7.