  The paper concerns the Gelfand-Kirillov dimension and the generating series
of nonsymmetric operads. An analogue of Bergman's gap theorem is proved,
namely, no finitely generated locally finite nonsymmetric operad has
Gelfand-Kirillov dimension strictly between $1$ and $2$. For every $r\in
\{0\}\cup \{1\}\cup [2,\infty)$ or $r=\infty$, we construct a single-element
generated nonsymmetric operad with Gelfand-Kirillov dimension $r$. We also
provide counterexamples to two expectations of Khoroshkin and Piontkovski about
the generating series of operads.
