"They're Biting," 1920,
drawing and oil
31.1 x 23.5 cm.
Seriously, go get a dictionary and look up "line" (n.) as it applies to drawing. The definition doesn't begin to describe mark-making and its possible dimensions. Webster's New World College Dictionary, Fourth Edition, provides 36 definitions for line as a noun, but only one comes close: "...a very thin, threadlike mark; specif., a long, thin mark made by a pencil, pen, chalk, etc." Klee's definition is much more accurate.
Still more about line tomorrow...