  A large number of Type IIIb-III pairs, in which the first component is a Type
IIIb burst and the second one is a Type III burst, are often recorded during
decameter Type III burst storms. From the beginning of their observation, the
question of whether the components of these pairs are the first and the second
harmonics of radio emission or not has remained open. We discuss properties of
decameter IIIb-III pairs in detail to answer this question. The components of
these pairs, Type IIIb bursts and Type III bursts, have essentially different
durations and polarizations. At the same time their frequency drift rates are
rather close, provided that the drift rates of Type IIIb bursts are a little
larger those of Type III bursts at the same frequency. Frequency ratios of the
bursts at the same moment are close to two. This points at a harmonic
connection of the components in IIIb-III pairs. At the same time there was a
serious difficulty, namely why the first harmonic had fine frequency structure
in the form of striae and the second harmonic did not have it. Recently Loi,
Cairns, and Li ( Astrophys. J. 790, 67, 2014) succeeded in solving this
problem. The physical aspects of observational properties of decameter IIIb-III
pairs are discussed and pros and cons of harmonic character of Type IIIb bursts
and Type III bursts in IIIb-III pairs are presented. We conclude that
practically all properties of the IIIb-III pair components can be understood in
the framework of the harmonic relation of the components of the IIIb-III pairs.
