Sentence:  A visit to the Parks, to the Embankment gardens, or the smokiest of the suburbs, reveals the fact that among evergreens—evergreens by courtesy, <WSD>everblacks</WSD> in reality—those which have the thickest, glossiest leaves are, other things being equal, least affected. 
Meaning of the word marked with <WSD> tags:  An evergreen tree that has very dark, colorless leaves or needles.