The effect of seed orientation on germination in a uniform environment: differential success without genetic or environmental variation
1995
Bosy, J. | Aarssen, L.W.
The seeds of eight herbaceous plant species were embedded in different orientations 2 mm below the surface of uniform agar. This was used to test whether seed orientation had any effect on germination without any physical heterogeneity in the germination medium. Seeds of Aster novae-angliae L., Cichorium intybus L., Daucus carota L., Galinsoga ciliata (Raf.) Blake and Potentilla recta L. showed less germination when the radicle was pointing vertically downward compared with other orientations. Orientation also affected the rate of germination of Galinsago ciliata and Cichorium intybus. Seeds of Lycopus unifloris Michx. and Erysmium cheiranthoides L. were not influenced by orientation. Seeds of Sonchus arvensis L. germinated poorly when buried, compared to surface-lying seeds. Responses of germination to seed orientation may reflect variation in the effects of gravity on the embryo depending on its position. Alternatively, uneven exposure to oxygen and light levels could have influenced results if different regions of the seed coat vary in their sensitivity to these factors. The results indicate that the experience of the environment for an individual seed can depend entirely on its orientation (which may occur by chance), even within a substrate that is completely homogeneous. This distinction of the roles of chance and environmental variation suggests the possibility that differences in success between neighbours within natural vegetation may not always be a consequence of either genetic or background environmental variation.
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