  The physical phenomena contributing to the galaxy growth can be tested all
the way to z= 1. Galaxy mass, extinction, star formation and gas metal
abundance can be measured in a robust way, as well as the distribution of the
galaxy morphologies. I discuss here the observational methods and their
accuracy. Physical quantities can be evaluated with uncertainties much lower
than 0.3 dex, if they are based on 2 sets of independent measurements. For
example, at a given IMF, the star formation rate is well estimated by combining
flux measurements of the extinction corrected Balmer line and of the mid-IR
continuum.
  Spiral mass growth had occurred from gas accretion and from merging. Gas
accretion can explain at most half of the spiral mass growth: at moderate
redshift, the numerous population of compact, merger and irregular galaxies
requires another origin. A spiral rebuilding scenario is able to reproduce all
the evolutionary trends observed since z~1, and could be at the origin of the
present-day, numerous population of early type spirals.
