The Securities and Exchange Commission has not necessarily reviewed the information in this filing and has not determined if it is accurate and complete.
The reader should not assume that the information is accurate and complete.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 13F

FORM 13F INFORMATION TABLE
OMB APPROVAL
OMB Number: 3235-0006
Estimated average burden
hours per response: 23.8
COLUMN 1 COLUMN 2 COLUMN 3 COLUMN 4 COLUMN 5 COLUMN 6 COLUMN 7 COLUMN 8
VALUE SHRS OR SH/ PUT/ INVESTMENT OTHER VOTING AUTHORITY
NAME OF ISSUER TITLE OF CLASS CUSIP (x$1000) PRN AMT PRN CALL DISCRETION MANAGER SOLE SHARED NONE
3M Company COM 88579y101 23,941 113,622 SH   SOLE   0 0 113,622
A T & T Inc New COM 00206r102 364 10,842 SH   SOLE   0 0 10,842
Abbott Labs COM 002824100 1,061 14,456 SH   SOLE   0 0 14,456
Abbvie Inc. Com COM 00287y109 1,791 18,933 SH   SOLE   0 0 18,933
Alphabet Inc Cap Sk Cl A COM 02079k305 507 420 SH   SOLE   0 0 420
Amazon.Com Inc COM 023135106 1,224 611 SH   SOLE   0 0 611
Apergy Corp Com COM 03755l104 613 14,077 SH   SOLE   0 0 14,077
Apple Computer COM 037833100 11,961 52,987 SH   SOLE   0 0 52,987
Auto Data Processing COM 053015103 32,015 212,496 SH   SOLE   0 0 212,496
Becton Dickinson COM 075887109 18,810 72,068 SH   SOLE   0 0 72,068
Bellicum Pharmaceutica COM 079481107 104 16,900 SH   SOLE   0 0 16,900
Berkshire Hathaway Cl B COM 084670702 482 2,252 SH   SOLE   0 0 2,252
Black Stone Minerals L Com Uni COM 09225m101 1,293 70,998 SH   SOLE   0 0 70,998
Bristol Myers Squibb COM 110122108 338 5,450 SH   SOLE   0 0 5,450
CVS Health COM 126650100 11,307 143,634 SH   SOLE   0 0 143,634
Chevron Corp COM 166764100 2,678 21,902 SH   SOLE   0 0 21,902
Coca-Cola COM 191216100 18,568 401,996 SH   SOLE   0 0 401,996
Dominion Energy Inc COM 25746U109 751 10,680 SH   SOLE   0 0 10,680
Donaldson COM 257651109 30,813 528,889 SH   SOLE   0 0 528,889
Dorchester Minerals LP COM 25820R105 1,490 73,023 SH   SOLE   0 0 73,023
Dover COM 260003108 19,556 220,896 SH   SOLE   0 0 220,896
Dow Dupont Inc Com COM 26078j100 354 5,503 SH   SOLE   0 0 5,503
Ecolab COM 278865100 27,355 174,483 SH   SOLE   0 0 174,483
Emerson Electric COM 291011104 20,805 271,680 SH   SOLE   0 0 271,680
Exxon Mobil Corp COM 30231g102 4,008 47,139 SH   SOLE   0 0 47,139
FedEx COM 31428x106 26,500 110,056 SH   SOLE   0 0 110,056
First Financial Bankshares COM 32020R109 217 3,668 SH   SOLE   0 0 3,668
Home Depot Inc COM 437076102 340 1,643 SH   SOLE   0 0 1,643
Honeywell International COM 438516106 21,007 126,243 SH   SOLE   0 0 126,243
Illinois Tool Works COM 452308109 27,779 196,849 SH   SOLE   0 0 196,849
Intel COM 458140100 25,734 544,173 SH   SOLE   0 0 544,173
International Business Machine COM 459200101 528 3,494 SH   SOLE   0 0 3,494
Intuitive Surgical Inc Com New COM 46120E602 560 975 SH   SOLE   0 0 975
Johnson & Johnson Com COM 478160104 24,803 179,511 SH   SOLE   0 0 179,511
Lowes Cos Inc COM 548661107 364 3,166 SH   SOLE   0 0 3,166
Luminex Corp COM 55027E102 1,075 35,453 SH   SOLE   0 0 35,453
Magellan Midstream Prt Unit Rp COM 559080106 474 7,000 SH   SOLE   0 0 7,000
Mastercard Inc Cl A COM 57636q104 255 1,147 SH   SOLE   0 0 1,147
McCormick COM 579780206 14,993 113,799 SH   SOLE   0 0 113,799
McDermott Intl Inc COM 580037109 440 23,863 SH   SOLE   0 0 23,863
Medtronic PLC COM g5960l103 649 6,593 SH   SOLE   0 0 6,593
Microsoft COM 594918104 44,250 386,906 SH   SOLE   0 0 386,906
National Instr COM 636518102 22,765 471,022 SH   SOLE   0 0 471,022
Netflix Inc COM 64110L106 251 670 SH   SOLE   0 0 670
Nokia COM 654902204 85 15,250 SH   SOLE   0 0 15,250
Nordson COM 655663102 36,508 262,834 SH   SOLE   0 0 262,834
Novartis AG COM 66987V109 17,043 197,807 SH   SOLE   0 0 197,807
Paccar COM 693718108 17,350 254,435 SH   SOLE   0 0 254,435
PepsiCo COM 713448108 19,544 174,811 SH   SOLE   0 0 174,811
Pfizer, Inc. COM 717081103 779 17,674 SH   SOLE   0 0 17,674
Phillips 66 COM COM 718546104 343 3,042 SH   SOLE   0 0 3,042
Procter & Gamble COM 742718109 17,907 215,150 SH   SOLE   0 0 215,150
Regeneron Pharmaceuticals Inc COM 75886F107 404 1,000 SH   SOLE   0 0 1,000
Sabine Royalty Trust UBI COM 785688102 591 14,000 SH   SOLE   0 0 14,000
San Juan Basin Royalty Trust COM 798241105 3,211 647,452 SH   SOLE   0 0 647,452
Schlumberger Ltd COM 806857108 11,703 192,099 SH   SOLE   0 0 192,099
Sysco Corp COM 871829107 350 4,774 SH   SOLE   0 0 4,774
Taiwan Semiconductor COM 874039100 2,754 62,362 SH   SOLE   0 0 62,362
Telefonica de Espana COM 879382208 222 28,192 SH   SOLE   0 0 28,192
United Parcel Svc Cl B COM 911312106 17,916 153,456 SH   SOLE   0 0 153,456
Verizon Communications COM 92343v104 223 4,168 SH   SOLE   0 0 4,168
Walt Disney COM 254687106 232 1,983 SH   SOLE   0 0 1,983
Waste Management Inc Del COM 94106L109 316 3,500 SH   SOLE   0 0 3,500