Do the atomic emission spectra provide supporting evidence for the wave or particle nature of electrons? My textbook states that the observation that a electric current passing through a gas causes characteristic emission spectrum to be observed gives supporting evidence for the wave nature of electrons.
I don't really understand why emission atomic spectra suggest the wave nature of electrons. Doesn't emission spectra give supporting evidence to Bohr's model of the atom, with orbiting electrons having quantised energies?
 A: Bohr's model is wrong.  A less-wrong model, which explains more of the data, is the Schroedinger wave equation, in which the electron is a wave.
However, a historian would point out that Bohr's hand-waving justification for quantized orbits was that an electron in a circular orbit with momentum $p$ would have de Broglie wavelength $\lambda = h/p$, and that an integer number of such waves must "fit" into the circular orbit.  The Bohr model is a wave model.
A: Let us disentangle two related types of experiments:

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*The atomic emission spectra are studied by observing the radiation emitted by atoms. Electric current here may serve as a means to bring the atoms in an excited state, as in a gas discharge lamp, but one can also use other techniques - e.g., optical excitation.

*In Frank-Hertz experiment: the electrons accelerated towards the anode collide with atoms. These collisions can be inelastic, if the energy of an electron is sufficiently high to excite atom to a higher energy state, the excited atom then loses the excess energy (most likely) via emission of a photon. What is measured here is however not the emission spectrum itself, but the electric current, which shows a characteristic sawtooth pattern, indicative of the discrete excitation energies in atoms.

What comes out in either type of the experiments, is that atoms have discrete energy states, which cannot be explained by classical theory. Originally, Bohr's model was an ad-hoc hypothesis to produce the correct atomic spectra by "fixing" the classical theory. As a more complete quantum theory became available, it became possible to justified Bohr's model prescriptions - they are derived as quasi-classical Bohr-Sommerfeld quantization rules (discussed in many QM texts).
