Document:

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                                                             Executed in 6 Parts
                                                           Counterpart No. (   )

                              NATIONAL EQUITY TRUST

                          TOP TEN PORTFOLIO SERIES 211

                            REFERENCE TRUST AGREEMENT

         This Reference Trust Agreement dated January 12, 2000 among Prudential
Securities Incorporated, as Depositor and The Chase Manhattan Bank, as Trustee,
sets forth certain provisions in full and incorporates other provisions by
reference to the document entitled "National Equity Trust Low Five Portfolio
Series, Trust Indenture and Agreement" (the "Basic Agreement") dated April 25,
1995. Such provisions as are set forth in full herein and such provisions as are
incorporated by reference constitute a single instrument (the "Indenture").

                                WITNESSETH THAT:

         In consideration of the premises and of the mutual agreements herein
contained, the Depositor and the Trustee agree as follows:

                                     Part I.

                     STANDARD TERMS AND CONDITIONS OF TRUST

         Subject to the provisions of Part II hereof, all the provisions
contained in the Basic Agreement are herein incorporated by reference in their
entirety and shall be deemed to be a part of this instrument as fully and to the
same extent as though said provisions had been set forth in full in this
instrument except that the Basic Agreement is hereby amended in the following
manner:

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                                       -2-

A.       Article I, entitled "Definitions", paragraph 22, shall be amended as
         follows:

         "Trustee shall mean The Chase Manhattan Bank
         or any successor trustee appointed as
         hereinafter provided."

B.       Article II, entitled "Deposit of Securities; Acceptance of Trust",
         shall be amended as follows:

         The second sentence of Section 2.03 Issue of Units shall be amended by
         deleting the words "on any day on which the Depositor is the only Unit
         Holder."

C.       Article III, entitled "Administration of Trust", shall be amended as
         follows:

         (i)      Section 3.01 Initial Costs shall be amended to substitute the
                  following language:

                  Section 3.01. Initial Cost The costs of organizing the Trust
                  and sale of the Trust Units shall, to the extent of the
                  expenses reimbursable to the Depositor provided below, be
                  borne by the Unit Holders, provided, however, that, to the
                  extent all of such costs are not borne by Unit Holders, the
                  amount of such costs not borne by Unit Holders shall be borne
                  by the Depositor and, provided further, however, that the
                  liability on the part of the Depositor under this section
                  shall not include any fees or other expenses incurred in
                  connection with the administration of the Trust subsequent to
                  the deposit referred to in Section 2.01. Upon notification
                  from the Depositor that the primary offering period is
                  concluded, the Trustee shall withdraw from the Account or
                  Accounts specified in the Prospectus or, if no Account is
                  therein specified, from the Principal Account, and pay to the
                  Depositor the Depositor's reimbursable expenses of organizing
                  the Trust and sale of the Trust Units in an amount certified
                  to the Trustee by the Depositor. If the balance of the
                  Principal Account is insufficient to make such withdrawal, the
                  Trustee shall, as directed by the Depositor, sell Securities
                  identified by the

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                  Depositor, or distribute to the Depositor Securities having a
                  value, as determined under Section 4.01 as of the date of
                  distribution, sufficient for such reimbursement. The
                  reimbursement provided for in this section shall be for the
                  account of the Unitholders of record at the conclusion of the
                  primary offering period and shall not be reflected in the
                  computation of the Unit Value prior thereto. As used herein,
                  the Depositor's reimbursable expenses of organizing the Trust
                  and sale of the Trust Units shall include the cost of the
                  initial preparation and typesetting of the registration
                  statement, prospectuses (including preliminary prospectuses),
                  the indenture, and other documents relating to the Trust, SEC
                  and state blue sky registration fees, the cost of the initial
                  valuation of the portfolio and audit of the Trust, the initial
                  fees and expenses of the Trustee, and legal and other
                  out-of-pocket expenses related thereto, but not including the
                  expenses incurred in the printing of preliminary prospectuses
                  and prospectuses, expenses incurred in the preparation and
                  printing of brochures and other advertising materials and any
                  other selling expenses. Any cash which the Depositor has
                  identified as to be used for reimbursement of expenses
                  pursuant to this Section shall be reserved by the Trustee for
                  such purpose and shall not be subject to distribution or,
                  unless the Depositor otherwise directs, used for payment of
                  redemptions in excess of the per-Unit amount allocable to
                  Units tendered for redemption. As directed by the Depositor,
                  the Trustee will advance funds to the Trust in an amount
                  necessary to reimburse the Depositor pursuant to this Section
                  and shall recover such advance from the sale or sales of
                  Securities at such time as the Depositor shall direct, but in
                  no event later than the termination of the Trust. Repayment of
                  any such advance shall be secured by a lien on the assets of
                  the Trust prior to the interest of the Unit Holders as
                  provided in Section 6.04.

         (ii)     The third paragraph of Section 3.05 Distribution shall be
                  amended to add the following sentence at the end thereof:

                  "The Trustee shall make a special distribution of the cash
                  balance in the Income and Principal accounts available for
                  such distribution to Unit

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                  Holders of record on such dates as the Depositor shall
                  direct."

         (iii)    The second to the last paragraph of Section 3.08 Sale of
                  Securities shall be amended to replace the word "equal" with
                  the following phrase: "be sufficient to pay."

D.       Reference to United States Trust Company of New York in its capacity as
         Trustee is replaced by the Chase Manhattan Bank throughout the Basic
         Agreement.

                                    Part II.

                      SPECIAL TERMS AND CONDITIONS OF TRUST

         The following special terms and conditions are hereby agreed to:

         A. The Trust is denominated National Equity Trust, Top Ten Portfolio
Series 211.

         B. The Units of the Trust shall be subject to a deferred sales charge.

         C. The contracts for the purchase of common stock listed in Schedule A
hereto are those which, subject to the terms of this Indenture, have been or are
to be deposited in Trust under this Indenture as of the date hereof.

         D. The term "Depositor" shall mean Prudential Securities Incorporated.

         E. The aggregate number of Units referred to in Sections 2.03 and 9.01
of the Basic Agreement is 250,000 as of the date hereof.

         F. A Unit of the Trust is hereby declared initially equal to
1/250,000th of the Trust.

         G. The term "First Settlement Date" shall mean January 19, 2000.

         H. The terms "Computation Day" and "Record Date" shall mean quarterly
on the tenth day of March, June, September, and December commencing March 10,
2000.

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         I. The term "Distribution Date" shall mean quarterly on the
twenty-fifth day of March, June, September, and December commencing March 25,
2000 or as soon thereafter as possible.

         J. The term "Termination Date" shall mean January 16, 2002.

         K. The Trustee's Annual Fee shall be $.95 (per 1,000 Units) for
100,000,000 and above units outstanding; $1.01 (per 1,000 Units) for
50,000,000 - 99,999,999 units outstanding; $1.05 (per 1,000 Units) for
49,999,999 and below units outstanding. In calculating the Trustee's annual fee,
the fee applicable to the number of units outstanding shall apply to all units
outstanding.

         L. The Depositor's Portfolio supervisory service fee shall be $.25 per
1,000 Units.

               [Signatures and acknowledgments on separate pages]

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         The Schedule of Portfolio Securities in Part A of the prospectus
         included in this Registration Statement for National Equity Trust, Top
         Ten Portfolio Series 211 is hereby incorporated by reference herein as
         Schedule A hereto.<PAGE>

                                   EXHIBIT 4.1

               CERTIFICATE OF DESIGNATIONS, RIGHTS AND PREFERENCES
                 SERIES B REDEEMABLE CONVERTIBLE PREFERRED STOCK

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                          CERTIFICATE OF DESIGNATIONS,

                             RIGHTS AND PREFERENCES

                                       OF

                 SERIES B REDEEMABLE CONVERTIBLE PREFERRED STOCK

                   (Pursuant to Section 151(g) of the General
                    Corporation Law of the State of Delaware)

         We, the undersigned duly authorized officers of AVITAR, INC., a
corporation organized and existing under the laws of the State of Delaware, do
hereby certify that:

         A. AVITAR, INC. (the "Corporation") was incorporated in the State of
Delaware on November 20, 1986.

         B. Pursuant to the authority conferred upon the Board of Directors of
the Corporation (the "Board of Directors") by the provisions of the
Corporation's Certificate of Incorporation, as amended (the "Certificate of
Incorporation"), and the provisions of Sections 141 and 151 of the General
Corporation Law of the State of Delaware, the Board of Directors has duly
adopted the following recitals and resolutions, which are not in conflict with
any provisions of the Certificate of Incorporation or the Corporation's By-Laws,
setting forth the number, terms, designations, relative rights, preferences,
privileges and restrictions of a series of Preferred Stock, par value $0.01 per
share, of the Corporation.

         WHEREAS, the Certificate of Incorporation provides for a class of
shares known as Preferred Stock, consisting of 5,000,000 shares;

         WHEREAS, the Certificate of Incorporation authorizes the issuance of
Preferred Stock from time to time in one or more series and authorizes the Board
of Directors to (a) determine or alter the rights, preferences, privileges and
restrictions granted to or imposed upon any wholly unissued series of Preferred
Stock, (b) fix the number of shares constituting any such series and
(c) determine the designation thereof; and

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         WHEREAS, the Corporation plans to issue a second series of Preferred
Stock and the Board of Directors desires to determine and fix the rights,
privileges, and restrictions relating to this series of Preferred Stock and the
number of shares constituting, and the designation of, such series.

         NOW, THEREFORE, BE IT RESOLVED, that the Board of Directors hereby
determines and fixes the designations of, the number of shares constituting, and
the rights, preferences, privileges and restrictions relating to, a second
series of Preferred Stock, as follows:

         1. Designation. 600,000 shares of Preferred stock shall be designated
hereby as "Series B Redeemable Convertible Preferred Stock" (hereinafter
referred to as the "Series B Preferred Stock") with the rights, preferences,
privileges and restrictions specified herein.

         2. Voting Rights. On all matters submitted to a vote of the holders of
the Corporation's common stock, par value $0.01 per share (the "Common Stock),
the holders of Series B Preferred Stock shall be entitled to exercise one vote
per share of Series B Preferred Stock.

         3. Dividends. The holders of Series B Preferred Stock shall be entitled
to receive, at the discretion of the Company, an annual 8% cash dividend or 10%
stock dividend computed on the amount invested in the Series B Preferred Stock.
Stock dividends shall be paid in shares of Series B Preferred Stock based on the
average closing price of ten (10) shares of the Common Stock for the five
trading days prior to the five days before the dividend is paid. Such dividend
shall be payable within ninety (90) days after the anniversary date of the
investment upon which the dividend is based.

         4. Liquidation Preference.

            A. Upon any voluntary or involuntary liquidation, dissolution or
winding-up of the Company, the holders of Series B Preferred Stock shall be
entitled to receive out of the assets of the Corporation which remain after
satisfaction in full of all valid claims of creditors of the Corporation,
liquidating distributions of an amount per share of Series B Preferred Stock
equal to the amount per share for Series B Preferred Stock paid by the holder
when making the investment. If these liquidation distributions are not paid in
full, the holders of the Series B Preferred Stock shall share ratably in any
distribution of assets in proportion to the full respective preferential amount
to which they are entitled.

            B. The merger or consolidation of the Corporation with or into any
other corporation and the sale or transfer of all or substantially all of the

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assets of the Corporation shall be deemed to be a dissolution, liquidation or
winding-up of the Corporation for the purposes of this Section 4.

            C. Written notices of any voluntary liquidation, dissolution or
winding-up of the Corporation, stating the payment date or dates when, and the
place or places where, the amounts distributable to holders of Series B
Preferred Stock in such circumstances shall be payable, shall be given by
first-class mail, postage pre-paid, mailed not less than twenty (20) days prior
to any payment stated therein, to the holders of Series B Preferred Stock, at
the address shown on the books of the Corporation or any transfer agent for the
Series B Preferred Stock.

            D. The Corporation may issue shares of its Preferred Stock which
have liquidation, dividend, voting, and/or redemption rights which are senior or
junior to, or pari passu with, the Series B Preferred Stock.

         5. Conversion.

            A. A holder of Series B Preferred Stock shall be entitled, at any
time prior to the close of business on any date fixed for the redemption of such
shares pursuant to Section 6 hereof, to cause any or all such shares to be
converted (the "Conversion") into ten shares of Common Stock for each share of
Series B Preferred Stock (the "Conversion Price"), subject to adjustment as
provided herein.

            B. The issuance by the Corporation of shares of Common Stock upon
any Conversion of shares of the Series B Preferred Stock made at the option of
the holder thereof, shall be effective the earlier of (i) the delivery to such
holder or such holders' designee of certificates representing the shares of
Common Stock issued upon Conversion thereof or (ii) the commencement of business
on the second business day after the surrender of the certificate or
certificates for the shares of Series B Preferred Stock to be converted, duly
assigned or endorsed for transfer to the Corporation ( or accompanied by duly
executed stock powers relating thereto) as provided hereby. On and after the
effective date of any Conversion, the converted shares of Series B Preferred
Stock shall no longer be deemed to be outstanding and all rights whatsoever with
respect thereto shall terminate, and the person or persons entitled to receive
the Common Stock issuable upon such Conversion shall be treated for all purposes
as the record holder or holders of such shares of Common Stock. All shares of
Series B Preferred Stock upon Conversion shall be restored to the status of
authorized but unissued shares of preferred stock without designation as to
Class, and may be issued thereafter.

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            C. The Conversion Price shall be subject to adjustment from time to
time as follows:

                  (i) If the Corporation shall, at any time or from time to time
         while shares of the Series B Preferred Stock shall be outstanding, (1)
         subdivide its outstanding shares of Common Stock into a greater number
         of shares, (2) combine its outstanding shares of Common Stock into a
         smaller number of shares or (3) pay a dividend (exclusive of the stock
         dividend provided herein), or make a distribution in Common Stock (or
         securities convertible into or exchangeable for shares of Common Stock)
         to holders of the Common Stock or other class or series of capital
         stock of the Corporation convertible into or exchangeable for shares of
         Common Stock, then the Conversion Price in effect immediately prior to
         such subdivision or combination, as the case may be, or immediately
         prior to the record date fixed for the determination of shareholders
         entitled to such dividend or distribution, shall be increased or
         decreased, as the case may be, to produce such results as would have
         been obtained prior to the occurrence of such event. An adjustment made
         pursuant hereto shall become effective immediately after the record
         date, in the case of a dividend or distribution payable in Common Stock
         (or other securities) and immediately after the effective date, in the
         case of a subdivision or combination.

                  (ii) If the Corporation shall, at any time or from time to
         time while shares of Series B Preferred Stock shall be outstanding,
         sell or issue rights, options, warrants or convertible securities
         containing the right to subscribe for or purchase shares of Common
         Stock at a purchase price less than the Conversion Price (i.e. 10% of
         the amount invested per share for Series B Preferred Stock), then the
         Conversion Price in effect immediately prior to such event shall be
         reduced by an amount equal to the quotient determined by dividing:

                  (a) an amount equal to the sum of (x) the product of the total
         number of shares of Common Stock outstanding immediately prior to the
         date of such sale or issuance of such rights, options, warrants or
         convertible securities and the Conversion Price in effect immediately
         prior to such sale or issuance, plus (y) the aggregate consideration
         (if non-cash consideration, the fair market value of which shall be
         determined by the Board of Directors in its good faith judgment), if
         any, received by the Corporation upon such sale or issuance; by

                  (b) the total number of shares of Common Stock outstanding
         immediately after such sale or issuance.

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               (iii) Whenever any adjustment is made in the Conversion Price
          pursuant to the foregoing provisions (i) or (ii), the Corporation
          shall, as soon as reasonably practicable thereafter, prepare a written
          statement signed by an executive officer of the Corporation setting
          forth the adjusted Conversion Price, determined as provided herein,
          and, in reasonable detail, the facts requiring such adjustment. The
          Corporation shall mail such statement to all holders of record of
          shares of Series B Preferred Stock at their respective addresses
          appearing on the stock records of the Corporation.

            D. The Corporation shall at all times reserve and keep available out
of its authorized and unissued Common Stock, solely for issuance upon the
Conversion of shares of Series B Preferred Stock as provided herein, free from
any preemptive rights, such number of shares of Common Stock as shall from time
to time be issuable upon the Conversion of all the shares of Series of Series B
Preferred Stock then outstanding.

         6. Redemption.

            A. In the event that the average of the last sales price ten shares
of Common Stock equal or exceeds 300% of the amount invested per share for
Series B Preferred Stock for any (20) consecutive trading days immediately prior
to the date of the notice discussed in Section 6.B below, the Corporation shall
have the right, at any time, to redeem all, or any portion of, the outstanding
shares of Series B Preferred Stock, at the price per share paid by the holder
upon making the investment in Series B Preferred Stock. If less than all of the
outstanding shares of Series B Preferred Stock shall be redeemed, the
Corporation shall redeem a pro rata portion of the shares of each holder. From
and after the date of redemption of any shares of Series B Preferred Stock, such
shares shall no longer be deemed to be outstanding and all rights in respect of
such shares of Series B Preferred Stock shall cease, except the right to receive
the redemption price.

            B. Notice of any redemption made pursuant to this Section 6 shall be
sent to the holders of Series B Preferred Stock at the address shown on the
books of the Corporation or any transfer agent for the Series B Preferred Stock
by first class mail, postage prepaid, mailed not less than thirty (30) days'
prior to the redemption date. Each notice shall state (i) the redemption date,
(ii) the total number of shares of Series B Preferred Stock to be redeemed and,
if fewer than all the shares held by such holder are to be redeemed, the number
of shares to be redeemed from such holder, (iii) the redemption price, (iv) the
place or places where certificates for such shares are to be surrendered for
payment of the redemption price and (v) Conversion rights of the shares to be
redeemed, the period within which Conversion

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rights may be exercised, and the Conversion Price and number of shares Common
Stock issuable upon Conversion of a share of Series B Preferred Stock at the
time. Promptly following receipt of such notice, the holders of Series B
Preferred Stock shall surrender their certificates representing such shares to
the Corporation unless they shall Convert in accordance with Sections 5 and 6
hereof.

            7. Registration Rights. The holders of Series B Preferred Stock
shall be entitled to "piggyback" registration rights with respect to such shares
on each occasion that the Corporation shall propose to file a registration
statement on Form S-3 (the "Registration Statement") under the Securities Act of
1933, as amended, covering any shares of Common Stock. The Corporation shall, at
least thirty (30) days before filing such Registration Statement, notify the
holders of Series B Preferred Stock in writing of such filing. For a period of
ten (10) days from the receipt of such notice, each holder of the Series B
Preferred Stock shall be entitled to provide written notice to the Corporation
of such holder's election to include in the Registration Statement up to the
number of Common Stock covered by his/her Series B Preferred Stock; provided,
however, that simultaneously with such notice, such holder shall agree to
Convert his/her shares of Series B Preferred Stock into Common Stock upon
effectiveness of the Registration Statement. The Corporation shall have the
right at any time thereafter to elect not to file any such Registration
Statement or to withdraw the same after filing but prior to the effective date
thereof. The Corporation shall pay all expenses relating to the Registration
Statement except sales commissions attributable to these securities and except
expenses incurred by the holders such as counsel for holders. Such sales
commissions and other expenses incurred by the holders shall be borne by the
holders.

            8. Pre-emptive Rights. The holders of Series B Preferred Stock shall
have no pre-emptive rights.

            9. Stated Capital. The amount to be capital at all times for each
share of Series B Preferred Stock shall be its par value (i.e., $0.01 per
share).

         RESOLVED, FURTHER, that the Chairman of the Board/Chief Executive
Officer and the Secretary of the Corporation be, and they are hereby are,
authorized and directed to prepare and file a Certificate of Designation in
accordance with this resolution and as required by law.

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         IN WITNESS WHEREOF, we have executed this Certificate of Designation
and affirm the foregoing as true under the penalties of perjury this 30thday of
April, 1998.

     /s/ J.C. Leatherman, Jr.                  /s/ Peter P. Phildius
---------------------------------           ------------------------------------
Secretary                                   Chairman of the Board/Chief
                                            Executive Officer

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