PETERSHAM, Mass. — Not every scientist would choose to spend a peaceful summer Sunday morning perched on a jittery scaffold 40 feet up a red oak tree, peering through a microscope to jab a leaf with a tiny glass needle filled with oil.

But Michael Knoblauch, a plant cell biologist at Washington State University, is in the stretch run of a 20-year quest to prove a longstanding hypothesis about how nutrients are transported in plants. He is also running out of time: He’s nearing the end of a sabbatical year, much of which he has spent here at Harvard Forest, a 3,500-acre research plot in central Massachusetts.

So he found himself up in the tree on a recent Sunday, accompanied by an assistant, his 19-year-old son, Jan, to collect more data for his research. While his son monitored the image from the microscope on a laptop, Dr. Knoblauch fiddled with a device that held the glass needle, manipulating it in minuscule increments as it entered the leaf. Though still attached to the tree, the leaf had been taped to the microscope’s stage, the little platform on which the specimen sits.

This kind of work is tediously difficult even in the calm of a laboratory, because the tip of the glass needle is delicate and tiny — far smaller than a human hair — and has to be impaled in a specific kind of cell. On the scaffold, vibrations make the job practically torturous. Even in the still early morning air, and even though the microscope sits on a device that senses the vibrations and counteracts them, Dr. Knoblauch and his son had to remain as motionless as possible.