Check out this poplar twig. When the growth hormones settle out, they create forward-thrusting bud casings around their large, folded leaves. When the fruiting hormones pile up behind them, they literally pile up in bursting flower shapes. Catkins will come, in the same shape.
And the twig behind? It is the flow that straightens out over the years behind this forward point of pressure, and thus it is straight. Amazing!