A Comparative Study of the Role of the Cotyledon in Seedling Development

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Abstract
Seedling development was studied in four species in which the cotyledons had different capacities for expansion and CO2-flxation. The highest growth-rates were shown by the two species in which the cotyledons showed the most expansion and also the greatest 14CO2-fixation capacity. Cotyledons of these species became very leaf-like and retained a high proportion of the radiocarbon fixation products during their growth in contrast to the hypogeal runner-bean cotyledon which had a high percentage export value although total fixation was low. Seedlings with leaf-like cotyledons which had the dual role of storage and subsequent provision of photosynthetic organs had delayed leaf development with early growth concentrated in cotyledon, hypocotyl, and root whereas species with cotyledons less well adapted for photosynthesis produced leaves at an earlier stage. Thus, the pattern of early seedling development was closely related to the degree of photosynthetic adaptation shown by the cotyledons. The evidence suggests that in the species studied, cotyledons adapted for the dual role appear to provide a more efficient system for early seedling development.

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