Tobacco mosaic virus

See vrbo.com/trust for details.

When a plant is infected with the tobacco mosaic virus, or TMV, its leaves develop yellow streaks and spots, eventually taking on a mosaic pattern.

Today we know, of course, that TMV is caused by a virus.

I mean, virus is in its name, and it's one that can spread as infected sap from one leaf comes in contact with another.

But toward the end of the 19th century, scientists didn't really know that viruses were a thing.

There was a vague sense that something like viruses could exist, but no confirmation, so TMV could have been caused by bacteria for all they knew.

So when a Russian scientist named Dmitri Ivanovsky ran the sap from a TMV-infected plant through a filter specially designed to prevent bacteria from passing through, the expectation was that the filtered sap would no longer be infectious.

Any leaves that came in contact with it should be fine.