This paper defines a new genus, the Cayley plane genus. By definition it is
the universal multiplicative genus for oriented Cayley plane bundles. The main
result (Theorem 2) is that it factors (tensor Q) through the product of the
Ochanine elliptic genus and the Witten genus-revealing a synergy between these
two genera-and that its image is the homogeneous coordinate ring
Q[Kum,HP^2,HP^3,CaP^2]/(CaP^3)\cdot(HP^3,CaP^2-(HP^2)^2) of the union of the
curve of Ochanine elliptic genera and the surface of Witten genera meeting with
multiplicity 2 at the point CaP^2=HP^3=HP^2=0 corresponding to the \^A-genus.
This all remains true if the word "oriented" is replaced with the word "spin"
(Theorem 3). This paper also characterizes the Witten genus (tensor Q) as the
universal genus vanishing on total spaces of Cayley plane bundles (Theorem 1, a
result proved independently by Dessai in [Dessai-2009].)