At least the inmates are a touch calmer

TOKYO - A Japanese prison is scrambling to eradicate marijuana plants that keep sprouting up on its exercise ground, officials said Tuesday.

The marijuana plants started sprouting at Abashiri Prison on Japan's northernmost island of Hokkaido about a year ago, said prison official Takeshi Okamura. He said officials plucked out as many as 300 marijuana plants and treated the ground last year, but several more sprouted again this year.

Prisoners reported them to the guards.

Officials believe the plants are wild.

"Apparently, somebody knew how to tell marijuana from other plants," Okamura said.

Local botanical experts concluded the marijuana seeds were inadvertently brought in with the soil used for the exercise ground, Okamura said.