(1) CO2, levels above 1,000 ppm repress expansion of the pileus and stimulate stipe growth in a wide variety of commercially-grown species, leading to spindly mushrooms in high CO2 conditions.(2) The development is initiated as a hyphal knot of 0.2 mm or less in diameter, which rapidly develops into a tiny primordium containing the rudimentary tissues of the future pileus and stipe.(3) Their compact pilei - tight-fitting in infant plants, robust and appetizingly domed in ripe ones - have a smooth (not lamellate) undersurface and a neat, strong stem.
