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                                                                    EXHIBIT 3.39

                          CERTIFICATE OF INCORPORATION
                                       OF
                              PTEX HOLDING COMPANY

     I, the undersigned, acting as incorporator of PTEX Holding Company, under
the General Corporation Law of Delaware, do hereby adopt the following
Certificate of Incorporation for such corporation.

First:    The name of the corporation is PTEX Holding Company.

Second:   The address of the corporation's registered office in the State of
          Delaware is Corporation Trust Center, 1209 Orange Street, City of
          Wilmington, County of New Castle, Delaware, and the name of its 
          registered agent at such address is The Corporation Trust Company.

Third:    The purpose of the corporation is to engage in any lawful act or
          activity for which Corporations may be organized under the General
          Corporation Law of Delaware.

Fourth:   The total number of shares that the corporation shall have authority
          to issue is 3,000 shares of common stock with a par value of $.01 per
          share.

Fifth:    No stockholder of this corporation shall, by reason of such person's
          holding stock of any class, have any preemptive or preferential right
          to purchase or subscribe to any stock of any class of this
          corporation, now or hereafter to be authorized, nor for any of its
          notes, debentures, bonds, or other securities, whether or not the
          issuance of such stock, or such notes, debentures, bonds, or other
          securities would adversely affect the dividend or voting rights of
          such stockholder, other than such rights, if any, as the board of 
          directors, in its discretion, may grant to the stockholders to
          purchase such additional securities; and the board of directors may
          issue treasury shares of any class of this corporation, or any notes,
          debentures, bonds, or other securities convertible into or of any
          class without offering the same in whole or in part to existing
          stockholders of any class.

Sixth:    Elections of directors need not be by written ballot except and to the
          extent provided otherwise in the bylaws of the corporation. Cumulative
          voting for the election of directors shall not be permitted.

Seventh:  The name and mailing address of the incorporator is T.L. Ford,
          Corporation Trust Center, 1209 Orange Street, County of New Castle,
          Wilmington, Delaware 19801.

Eighth:   The number of directors constituting the initial board of directors is
          three and the names and addresses of such persons serving as directors
          until the first annual meeting of stockholders or until such persons'
          successors shall be elected and qualified are:
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            Charles M. Hansen, Jr.        4111 Mint Way, Dallas, Texas 75237
            Ronald M. Wehtje              4111 Mint Way, Dallas, Texas 75237
            Charles H. Slaybaugh          222 Delaware Ave., 17th Floor,
                                          Wilmington, Delaware 19801


Ninth:      The corporation shall have perpetual existence.

Tenth:      The board of directors is expressly authorized to make, alter, or
            repeal the bylaws of the corporation.

Eleventh:   A director of the corporation shall not be personally liable to the
            corporation or its stockholders for monetary damages for breach of
            fiduciary duty as a director, except for liability (i) for any
            breach of the director's duty of loyalty to the corporation or its
            stockholders, (ii) for acts or omissions not in good faith or that
            involve intentional misconduct or a knowing violation of law, (iii)
            under Section 174 of the Delaware General Corporation Law, as the
            same exists or hereafter may be amended, or (iv) for any transaction
            from which the director derived an improper personal benefit. If the
            Delaware General Corporation Law hereafter is amended to authorize
            the further elimination or limitation of the liability of directors,
            then the liability of a director of the corporation, in addition to
            the limitation on personal liability provided herein, shall be
            limited to the fullest extent permitted by the amended Delaware
            General Corporation Law. Any repeal or modification of this
            paragraph by the stockholders of the corporation shall be 
            prospective only, and shall not adversely affect any limitation on
            the personal liability of a director of the corporation existing at
            the time of such repeal or modification.

Twelfth:    The undersigned incorporator, for the purpose of forming a
            corporation pursuant to the General Corporation Law of Delaware,
            does hereby declare and certify that the foregoing Certificate of
            Incorporation is such person's act and deed and that the facts
            herein stated are true, and accordingly, has hereunto set such
            person's hand this 20th day of March, 1996.


                                        /s/  T. L. FORD
                                        --------------------
                                        T. L. Ford


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