Great job on these dissection Anne! I love the two stamens in the Olive family (Oleaceae) for the lilac. Always makes me wonder how they manage with so fewer stamens, but they are very proliferous and seem to set seeds just fine. Perhaps they cope with having a very strong scent, and potentially nectar to offer the bees as a pollination reward. I think the placentation of the rose is either marginal or apical. Remember each of the tiny ovules has its own style, so the rose hip is an aggregate of achenes plus it is accessory since the receptacle is enlarged. So you would need to look at each of the tiny roundish achenes to see what the placentation there is. I think they are single-seeded achenes, and the ovule in each achene is either attached at the base (basal) placentation or at the margin where the carpel is fused.
Great job on these dissection Anne! I love the two stamens in the Olive family (Oleaceae) for the lilac. Always makes me wonder how they manage with so fewer stamens, but they are very proliferous and seem to set seeds just fine. Perhaps they cope with having a very strong scent, and potentially nectar to offer the bees as a pollination reward. I think the placentation of the rose is either marginal or apical. Remember each of the tiny ovules has its own style, so the rose hip is an aggregate of achenes plus it is accessory since the receptacle is enlarged. So you would need to look at each of the tiny roundish achenes to see what the placentation there is. I think they are single-seeded achenes, and the ovule in each achene is either attached at the base (basal) placentation or at the margin where the carpel is fused.