Fiber class of a rational normal scroll
= Fiber class of a rational normal scroll
{title2=$L=\pi^*\mathcal O_{\mathbb P^1}(1)$}
The divisor class of a fibre of the ruling of a <rational normal scroll> has square zero. Its complete pencil recovers the projection to $\mathbb P^1$, and its intersection with $M^{n-1}$ is one.