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The relationship between seed weight, embryo weight, ash content and maximum size attained by seedlings dependent on their own food reserves was investigated in 24 species of Compositae. The fraction of total seed weight contributed by the seed coat increased with seed weight from 15% in Erigeron canadensis to 61% in Tragopogon pratensis. Seedling weight was proportional to embryo weight raised to the power of 2/3. That is, the larger the embryo the less carbon it assimilated per unit weight of embryo. The relative growth rate of the seedlings during the first 3 weeks was inversely proportional to ln embryo weight. The root weight ratios of the seedlings were inversely proportional to ln embryo weight. The ash content of the seeds was negatively correlated with their weight but absolute mineral content per seed was directly proportional to maximum seedling size attained, regardless of seed size. It is postulated that the relatively larger seed coats of big seeds are a defence against increased risk of predation. The ash contents and root weight ratios of the seedlings suggest that the growth of small seedlings is limited by soil nutrients and that of large seedlings by light.
The New Phytologist © 1983 New Phytologist Trust