Assimilation Rates of Some Woodland Herbs in Ontario

The assimilation characteristics of about 30 species of common woodland herbs have been investigated using an infrared gas analyzer. The species, on the basis of these characteristics, were divided into three groups termed "shade tolerant," "shade intolerant," and an intermediate group, "semi-shade tolerant." There was a correlation between the time of leaf emergence and expansion and the assimilation characteristics of the species, with shade-intolerant species developing during the early part of the year in high light intensities and the shade-tolerant species developing after the expansion of the canopy. Leaves of the semi-shade-tolerant group developed during the expansion of the canopy and were the most variable. Adaptation of the leaves to different light intensities is discussed.