At first I thought the question was rather like "Who’s buried in Grant’s Tomb?" The correct answer isn’t all that easy to discover, I find. Apparently, there was a botanist named J. A. L. W. Knop who came up with the solution sometime in the 1860s. More than that, I cannot tell.

Knop’s Solution

Dissolve each of the following four salts in one liter of distilled water:

1 g potassium nitrate (KNO3)

1 g magnesium sulfate (MgSO4)

1 g potassium phosphate dibasic (K2HPO4)

3 g calcium nitrate (Ca(NO3)2)

For immediate use, add five liters of distilled water to the original stock solution. This 1% solution may need to be shaken before use to mix undissolved salts. Pour solution into containers and autoclave.