We give a new proof of the existence (\cite{HM}, \cite{Ren}) of a
Jenkins-Strebel differential Φ on a Riemann surface \SR with prescribed
heights of cylinders by considering the harmonic map from \SR to the leaf
space of the vertical foliation of Φ, thought of as a Riemannian graph.
The novelty of the argument is that it is essentially Riemannian as well as
elementary; moreover, the harmonic maps existence theory on which it relies is
classical, due mostly to Morrey (\cite{Mo}).Comment: 8 pages, 2 figures available upon reques