The measurements of methane emission by leaves torn off from greenhouse plants and Siberian stone pine needles, obtained with the help of a laser methane detector based on a 1.65 μm tunable diode laser, are presented. The emission was estimated via comparison of the methane concentration in the room air with its concentration in a closed incubation volume containing the torn off leaves. The accumulation time varied between 10 and 300 hours. It is shown that in spectrometric measurements of the methane emission by green mass, the ethylene emission by damaged plants should be taken into account. The ethylene has absorption lines near the methane ones. This was not taken into account in previous measurements of the methane concentration. The obtained rate of methane emission by the green mass is significantly lower (1.6-8.7) • 10-12 kg/(g • h) then the reported by other researchers.