K_{l 3} and pi_{e 3} transition form factors

$K_{ell 3}$ and $pi_{e 3}$ transition form factors are calculated as an application of Dyson-Schwinger equations. The role of nonanalytic contributions to the quark--W-boson vertex is elucidated. A one-parameter model for this vertex provides a uniformly good description of these transitions, including the value of the scalar form factor of the kaon at the Callan-Treiman point. The $K_{ell 3}$ form factors, $f_pm^K$, are approximately linear on $tin [m_e^2,m_mu^2]$ and have approximately the same slope. $f_-^K(0)$ is a measure of the Euclidean constituent-quark mass ratio: $M^E_s/M^E_u$. In the isospin symmetric limit: $-f_+^pi(0)= F_pi(t)$, the electromagnetic pion form factor, and $f_-^pi(t)equiv 0$.