two-branch tree radical (no. 115)
禾 centers on a grain-bearing plant, especially rice, with a drooping head of grain. As a radical, it appears in characters related to grain, harvest, or agricultural concepts.
禾 is a pictograph of a grain plant with a heavy drooping head. The top stroke represents the bent grain head, and the lower part resembles the stalk and roots.
The top stroke is a bent grain head, and the rest is the stalk and roots. Picture a rice plant heavy with grain, bending over: 禾 is grain.
For カ, imagine a car (カ) driving through a field of ripe grain, the stalks bending under the weight.