.-
Looking for info on a paper back novel that's at least pre 90s. Main story is alien race building rockets with plant pods as engines. Continually have extinction level events and have to restart building their civilization.
I'm still holding out for the crucible of time by Brunner. (copyright 1982/1983, originally published in two parts in Isaac Asimov's Science Fiction Magazine)Dug my copy out and:-
Alien race, definitely. No skeleton, pumped up by hydraulics, more or less. reproduce by budding. Allergic to metals.
Series of meteor strikes, not quite extinction level (or there'd be no beings to restart over, but definitely civilisation destroying. Thir stellar system is drifting into a region of cosmic junk. Successive waves of progress come from different cultures, as the previous societies are exterminated.
They start with astronomy, and the discovery of the New Star, then optics, with Jing and Keepfire, have biological crises as well as physical ones, and finish by drifting away from the planet in sort of pressurised green houses, habitats in which they can miss out on the planetary bombardments.
Just too close to the specified story line.