  Establishing the relative role of internally and externally driven mechanisms
responsible for disc and bulge growth is essential to understand the evolution
of disc galaxies. In this context, we have studied the physical properties of
disc galaxies without classical bulges in comparison to those with classical
bulges since z~0.9. Using images from the Hubble Space Telescope and Sloan
Digital Sky Survey, we have computed both parametric and non-parametric
measures, and examined the evolution in size, concentration, stellar mass,
effective stellar mass density and asymmetry. We find that both disc galaxies
with and without classical bulges have gained more than 50% of their present
stellar mass over the last ~8 Gyrs. Also, the increase in disc size is found to
be peripheral. While the average total (Petrosian) radius almost doubles from
z~0.9 to z~0, the average effective radius undergoes a marginal increase in
comparison. Additionally, increase in the density of the inner region is
evident through the evolution of both concentration and effective stellar mass
density. We find that the asymmetry index falls from higher to lower redshifts,
but this is more pronounced for the bulgeless disc sample. Also, asymmetry
correlates with the global effective radius, and concentration correlates with
the global Sersic index, but better so for higher redshifts only. The
substantial increase in mass and size indicates that accretion of external
material has been a dominant mode of galaxy growth, where the circumgalactic
environment plays a significant role.
