View of medical marijuana plants. (Linda Davidson/The Washington Post)

Among marijuana’s unique properties, the way it illuminates racial disparities stands out.

Take arrests for marijuana possession. Even though there is minimal difference in the amount of marijuana used by blacks and whites, blacks are four times more likely than whites to be arrested for smoking pot, according to a 2013 study by the American Civil Liberties Union.

The disparities in Maryland and the District were among the highest in the nation, with blacks up to eight times more likely than whites to be arrested.

On the other hand, when it comes to getting a lucrative marijuana grower’s license, you can hardly find a black person at all.

These disparities don’t occur by happenstance. They are evidence of institutional racism, which many readers have tried to dismiss as, according to one, “just a vague excuse for any measurement by which blacks on average don’t do as well as whites on average.”

The marijuana issue roiling in Maryland sheds light on how institutional racism works. And there is nothing vague about it.

There were 145 applicants for licenses to grow medical marijuana. Despite a state law requiring racial diversity in licensing, none of the 15 firms selected to start growing marijuana this summer are owned by African Americans. Turns out, the commission set up to award the licenses decided to ignore racial diversity in favor of “geographic diversity,” which just happened to produce the all-white outcome.

Now that state is contending with allegations that the process was tainted. The scoring system that was used to select applicants was cast into doubt by reports of conflicts of interest, including revelations that one of the evaluators knew one of the applicants. Two firms had their scores boosted in the interest of creating “geographic diversity.”

Some white-owned firms allege that licenses were given to unqualified white growers. A black-owned firm staffed with experienced black doctors, lawyers and scientists was passed over.

The commission does not say why one firm is chosen over another.

So why didn’t the commission just follow the law?

According to commissioners, the state attorney general’s office advised that evidence of racial disparity — in this or another comparable industry — was necessary before such a “preference” could pass constitutional muster. In other words, they would have to wait until after black applicants were passed over to see if they were discriminated against.

Meanwhile, white growers could corner the market. By the time the black growers finished filing legal pleas and appeals, the economic opportunities could be reduced to operating bong shops and cannabis cookie boutiques.

The commission said there could be future opportunities when it considers issuing more cultivation licenses in 2018 — “if supply doesn’t meet demand.”

Gov. Larry Hogan (R) ordered his administration to study racial disparities in the medical marijuana industry to see if racial preferences can be justified.

Maryland is 31 percent black. Even a focus on “geographic diversity” should have resulted in the selection of a qualified black-owned firm.

Through the lowly marijuana plant, we can see how laws and policies supposedly meant to promote economic opportunity for all frequently don’t.

Even in the District, with its black mayor and with black residents making up the largest group of residents, the impact of institutional racism is hardly blunted.

In 2015, D.C. voters legalized marijuana for personal use. The reform was billed as a way to reduce the racial disparities in drug arrests. But there were caveats — fine print, if you will — crafted in ways that did more to protect whites who wanted the freedom to smoke than the blacks whose plights had been used to get the laws passed.

Under the new laws, you could smoke, but only in your home. Not outdoors. For those living in apartments and public housing, where smoking is prohibited, nothing had really changed. The same draconian laws that underpinned the “war on drugs” were still in effect for them.

In a one-year period since legalization took effect, arrests for smoking marijuana in public jumped from 142 to 400, according to D.C. police data. If the trend holds, there will be at least as many — if not more — arrests this year. Arrests for selling marijuana have also tripled, from 80 in 2015 to 220 in 2016, police said

And if that trend holds, there will be at least as many if not more arrests for selling and smoking in public in 2017 as there were last year.

Adam Eidinger, who spearheaded the drive to legalize marijuana in the District, has noted that some apartment dwellers fear that management will respond to smoking violations by providing less maintenance. He cited one resident who says she had been targeted for harassment by management because she uses marijuana, as prescribed by doctors, for treatment of her fibromyalgia.

“The resident also worries that developers might be setting the stage for mass evictions as the area gentrifies from the Anacostia extension of the D.C. Streetcar,” Eidinger wrote in an opinion piece for The Washington Post earlier this year.

Roger B. Taney, a Maryland native and former chief justice of the U.S. Supreme Court, had asserted in 1857 that blacks were never intended to have the same rights and privileges as whites. In writing for the majority in the Dred Scott case, Taney reinforced the racist notion that blacks were a “subordinate and inferior class of beings.” Furthermore, white people could never be blamed or expected to compensate for the subjugation and exclusion because that’s what the slaveholding Founding Fathers intended.

In celebration of his views, Maryland lawmakers erected a statue of Taney on the grounds of the Maryland State House in Annapolis. And there it stayed, for nearly 150 years, until last week. In the wake of a violent neo Nazi and Ku Klux Klan gathering in Charlottesville, the statue was finally removed.

But vestiges of the institutional racism that Taney championed remain.

Maryland State Delegate Cheryl Glenn, chair of the 51-member Legislative Black Caucus, said of the decision to exclude blacks and license only white marijuana growers: “Nothing changes, and most importantly, that means African Americans are left out of this billion-dollar industry in Maryland.”

Not left out, kept out.

And you don’t need a toke of weed to see it.

To read previous columns, go to washingtonpost.com/milloy.