  Let $\M_{k}^{n}$ be the moduli space of based (anti-self-dual) instantons on
$\cpbar$ of charge $k$ and rank $n$. There is a natural inclusion of rank $n$
instantons into rank $n+1$. We show that the direct limit space is homotopy
equivalent to $BU(k)\times BU(k)$. The moduli spaces also have the following
algebro-geometric interpretation: Let $\linf$ be a line in the complex
projective plane and consider the blow-up at a point away from $\linf$. $\M
_{k}^{n}$ can be described as the moduli space of rank $n$ holomorphic bundles
on the blownup projective plane with $c_{1}=0$ and $c_{2}=k$ and with a fixed
holomorphic trivialization on $\linf$.
