I also received this Things of Science unit without the “things”. Page 4 in the booklet (see below) lists the few things you would need to purchase to recreate this unit— a few packets of seeds, a pH indicator and a few chemicals that shouldn’t be difficult to source.
They mention the term hydroponics, and that is the term I had always heard for growing plants soilless. In the 70’s, with people turning their minds both to distant space travel and over population — with the likes of films like (Logan’s Run, Soylent Green and SilentRunning) I often associated the term hydroponics to some sort of future farming, or perhaps growing food on the moon….
I see no reason why hydroponics is any less relevant today as it was in 1968 when this unit was first created.
Scan of the booklet (this is a big booklet, by the way — lots of content):
(Mention of the kit in an old newspaper.)