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 21,598 113,350 SH   SOLE   0 0 113,350
A T & T Inc New COM 00206r102 302 10,592 SH   SOLE   0 0 10,592
Abbott Labs COM 002824100 1,035 14,314 SH   SOLE   0 0 14,314
Abbvie Inc. Com COM 00287y109 1,746 18,943 SH   SOLE   0 0 18,943
Alphabet Inc Cap Sk Cl A COM 02079k305 423 405 SH   SOLE   0 0 405
Amazon.Com Inc COM 023135106 972 647 SH   SOLE   0 0 647
Apple Computer COM 037833100 8,216 52,087 SH   SOLE   0 0 52,087
Auto Data Processing COM 053015103 27,703 211,282 SH   SOLE   0 0 211,282
Becton Dickinson COM 075887109 16,216 71,967 SH   SOLE   0 0 71,967
Bellicum Pharmaceutica COM 079481107 41 13,900 SH   SOLE   0 0 13,900
Berkshire Hathaway Cl B COM 084670702 455 2,227 SH   SOLE   0 0 2,227
Black Stone Minerals L Com Uni COM 09225m101 1,099 70,998 SH   SOLE   0 0 70,998
Bristol Myers Squibb COM 110122108 283 5,450 SH   SOLE   0 0 5,450
CVS Health COM 126650100 9,490 144,845 SH   SOLE   0 0 144,845
Chevron Corp COM 166764100 2,383 21,906 SH   SOLE   0 0 21,906
Coca-Cola COM 191216100 18,875 398,618 SH   SOLE   0 0 398,618
Dominion Energy Inc COM 25746U109 643 9,000 SH   SOLE   0 0 9,000
Donaldson COM 257651109 22,727 523,794 SH   SOLE   0 0 523,794
Dorchester Minerals LP COM 25820R105 1,069 73,023 SH   SOLE   0 0 73,023
Dover COM 260003108 15,577 219,546 SH   SOLE   0 0 219,546
Dow Dupont Inc Com COM 26078j100 281 5,259 SH   SOLE   0 0 5,259
Ecolab COM 278865100 25,574 173,557 SH   SOLE   0 0 173,557
Emerson Electric COM 291011104 16,000 267,789 SH   SOLE   0 0 267,789
Exxon Mobil Corp COM 30231g102 3,091 45,336 SH   SOLE   0 0 45,336
FedEx COM 31428x106 17,730 109,899 SH   SOLE   0 0 109,899
First Financial Bankshares COM 32020R109 212 3,668 SH   SOLE   0 0 3,668
Home Depot Inc COM 437076102 284 1,652 SH   SOLE   0 0 1,652
Honeywell International COM 438516106 16,572 125,435 SH   SOLE   0 0 125,435
Illinois Tool Works COM 452308109 24,833 196,014 SH   SOLE   0 0 196,014
Intel COM 458140100 25,443 542,157 SH   SOLE   0 0 542,157
International Business Machine COM 459200101 358 3,149 SH   SOLE   0 0 3,149
Intuitive Surgical Inc Com New COM 46120E602 467 975 SH   SOLE   0 0 975
Johnson & Johnson Com COM 478160104 22,968 177,977 SH   SOLE   0 0 177,977
Lowes Cos Inc COM 548661107 293 3,168 SH   SOLE   0 0 3,168
Luminex Corp COM 55027E102 809 34,999 SH   SOLE   0 0 34,999
Magellan Midstream Prt Unit Rp COM 559080106 399 7,000 SH   SOLE   0 0 7,000
Mastercard Inc Cl A COM 57636q104 216 1,147 SH   SOLE   0 0 1,147
McCormick COM 579780206 15,663 112,487 SH   SOLE   0 0 112,487
McDermott Intl Inc COM 580037109 156 23,863 SH   SOLE   0 0 23,863
Medtronic PLC COM g5960l103 602 6,623 SH   SOLE   0 0 6,623
Microsoft COM 594918104 38,941 383,392 SH   SOLE   0 0 383,392
National Instr COM 636518102 21,217 467,532 SH   SOLE   0 0 467,532
Nokia COM 654902204 89 15,250 SH   SOLE   0 0 15,250
Nordson COM 655663102 31,208 261,484 SH   SOLE   0 0 261,484
Novartis AG COM 66987V109 16,916 197,136 SH   SOLE   0 0 197,136
Paccar COM 693718108 14,447 252,828 SH   SOLE   0 0 252,828
PepsiCo COM 713448108 19,236 174,109 SH   SOLE   0 0 174,109
Pfizer, Inc. COM 717081103 749 17,164 SH   SOLE   0 0 17,164
Phillips 66 COM COM 718546104 262 3,042 SH   SOLE   0 0 3,042
Procter & Gamble COM 742718109 19,621 213,458 SH   SOLE   0 0 213,458
Sabine Royalty Trust UBI COM 785688102 522 14,000 SH   SOLE   0 0 14,000
San Juan Basin Royalty Trust COM 798241105 3,108 647,452 SH   SOLE   0 0 647,452
Schlumberger Ltd COM 806857108 5,505 152,577 SH   SOLE   0 0 152,577
Sysco Corp COM 871829107 277 4,426 SH   SOLE   0 0 4,426
Taiwan Semiconductor COM 874039100 5,641 152,835 SH   SOLE   0 0 152,835
Telefonica de Espana COM 879382208 239 28,192 SH   SOLE   0 0 28,192
United Parcel Svc Cl B COM 911312106 14,895 152,727 SH   SOLE   0 0 152,727
Verizon Communications COM 92343v104 261 4,648 SH   SOLE   0 0 4,648
Walt Disney COM 254687106 242 2,208 SH   SOLE   0 0 2,208
Waste Management Inc Del COM 94106L109 311 3,500 SH   SOLE   0 0 3,500