Definition of "glasshouse"

The highway to the East Coast which ran through the borough of Ebbfield had always been a main road and even now, despite the vast garages, the pylons and the gaily painted factory glasshouses which had sprung up beside it, there still remained an occasional trace of past cultures.

1963, Margery Allingham, chapter 7, in The China Governess: A Mystery, London: Chatto & Windus