The book is most probably wrotten in UK. Syrange is a manual piston type sprayer and mister for water or chemical spray.

It was apparently common practice in those days to rinse or spray the leaves with water every day for control of spider mites and possibly other pests. One concern I'd have with that practice is that water control is very essential in a greenhouse for optimum fruit eating quality. A controlled water deficit improves quality of stone fruit. I'm not so sure about figs and berries. But I'm fairly certain too much water isn't good for fig eating quality.

In my greenhouse even keeping humidity as low as possible, it is easy to over water at the expense of fruit quality. For in-ground trees I'm only applying about 1 inch water every 10 days, 30 inches annual for a 300+ day growing season.

I would love to have a green house for fig trees someday.
Terry