Importance of Photosynthetic Cotyledons for Early Growth of Woody Angiosperms

At various times after seed germination, epigeous cotyledons were excised or treated with DCMU (3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea) to inhibit cotyledon photosynthesis of seedlings of Acer negundo L., Ailanthus altissima (Mill.) Swingle, Eucalyptus globulus Labill., Fraxinus pennsylvanica Marsh., Robinia pseudacacia L., and Ulmus americana L. In all species, DCMU inhibited expansion of cotyledons, elongation of roots, initiation of lateral roots, and expansion of foliage leaves. During the first 10 days after radicle emergence decotylization also variously inhibited growth of plant parts. Photosynthetic rates per cotyledon varied among species in the following order: Robinia pseudacacia > Ailanthus altissima ≥ Fraxinus pennsylvanica > Ulmus americana . The length of time that cotyledon photosynthesis contributed to growth of axial parts varied widely among species.