A little checking and,
voilá, Boyd explains it all:
(The Library of America,
page 802 on Ada,II, page 319)
Quercus
ruslan Chât.
Nabokov wrote to Bobbie Ann
Mason: "The specific name of this invented tree alludes to the beginning of
Pushkin's long poem Ruslan and Lyudmilla (1820) where there is a cat
(chat in French) walking on a golden chain around a fairytale oaktree. The oak
in Ada is supposed to have been described by a botanist named Châtel (or
Châtelet or Château-Lafite) abbreviated to Chât. after the specific
ruslan. The distorted shadow of Chateaubriand should not interfere with
the flash of the Ruslan-oak-cat recognition."
No reference to
grottesque subliminar effects with grotto, fountain and papapissing and Lol's
browninan pipapassing, which also happens in the proximity of the
lines about the Quercus ruslan Chât.
Actually, in
Lolita, following A. Appel Jr., there is an explanation
about bladders and pissing, under "fountainism" or "undinism" (undine:
mermaid).
In SM we learn
that Mademoiselle's room carried a faint smell of urine, and, in Ada,
Mlle la Rivière is once described while she is urinating in a river during a
picnic.
The passing-pisser in
Pale Fire, connected to barn (not burn), papa and King, is
a gardener.
Apparently gardeners are
more important than I surmised at first (with frequent cameo appearances
and left over beer cans)