pistil, stamen
蕋 centers on the reproductive parts of a flower: the pistil and stamen. It is a specialized botanical kanji for these flower organs.
蕋 is a variant form of 蕊. It combines the plant radical 艹 with 歮, which likely represents the clustered appearance of stamens and pistils. The exact historical development of the lower component is uncertain.
The grass top 艹 marks a plant, and the lower part 歮 looks like a cluster of three small things with lines inside, like the tiny pistils and stamens inside a flower.
For ズイ, imagine a bee zooming into a flower to reach the pistil: zoom -> ズイ, and the bee lands right on the 蕋.