The name Betula alba is a good marker for an obsolete book or site.

I realize that the correct name is B. pendula, but that doesn't help. Some
authorities list 'Trost's Dwarf' as a cultivar of B. pendula, others simply as
a Betula cultivar. According to the botanist at Hillier Gardens, 'Trost's
Dwarf' has downy shoots, which makes him think it is not B. pendula. They don't
have the plant any more, so he has no further information.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)