  A planar monomial is by definition an isomorphism class of a finite, planar,
reduced rooted tree. If $x$ denotes the tree with a single vertex, any planar
monomial is a non-associative product in $x$ relative to $m-$array grafting. A
planar power series $f(x)$ over a field $K$ in $x$ is an infinite sum of
$K-$multiples of planar monomials including the unit monomial represented by
the empty tree. For every planar power series $f(x)$ there is a universal
differential $d f(x)$ which is a planar power series in $x$ and a planar
polynomial in a variable $y$ which is the differential $d x$ of $x$. We state a
planar chain rule and apply it to prove that the derivative
$\frac{d}{dx}(Exp_k(x))$ is the $k-$ary planar exponential series. A special
case of the planar chain rule is proved and it derived that the planar universe
series $Log_k (1+x)$ of $Exp_k(x)$ satisfies the differential equation
$\biggl((1+x) \frac{d}{dx}\biggl)(Log_k(1+x)) = 1$ where $(1+x) \frac {d}{dx}$
is the derivative which when applied to $x$ results in $1 + x.$
