 "land that is used principally as an ecological laboratory by a public or  private college or university."   II.   At oral argument, we questioned whether the District possessed authority to  challenge the constitutionality of section 00.00(0) of the Code, an integral part of the statutory  scheme entrusted by the legislature to the District's administration.  See Aransas County Appraisal  Review Bd. v. Texas Gulf Shrimp Co., 000 S.W.0d 000, 000 (Tex. App.--Corpus Christi 0000,  writ ref'd n.r.e.) (tax assessors are proper parties to challenge constitutionality of tax-code  provisions); Colony Mun. Util. Dist. No. 0 v. Appraisal Dist., 000 S.W.0d 000, 000 (Tex.  App.--Dallas 0000, writ ref'd n.r.e.) (because rights of equal protection and due process of law  are vested only in persons, not political subdivisions, appraisal district may not challenge  constitutionality of tax-code provisions).  We are grat