Hunched over a microscope, Steve Cottrell peered at a bud from a plant that is increasingly used as medicine in Arizona and across the nation.

He pointed at a computer screen that glowed with a magnified image of the marijuana bud. The sample, the size of a quarter, was covered with powdery white bumps — a mold that was invisible to the naked eye.

Increasingly, medical-marijuana dispensaries and patients are turning to laboratories to evaluate medical-marijuana plants, identify potentially harmful substances and pinpoint the potency of plants and cannabis-infused products, from caramels and “cherry roll” candies to butter.

Cottrell, 42, and his company, AZ Med Testing, is one of a number of labs in the state that cater to the burgeoning medical-marijuana industry. The lab, located in a small office complex in north-central Phoenix, works with about a third of the state’s 70-plus dispensaries, he says.

Read more: Medical marijuana purity under a microscope | Arizona Republic