The author has had an experiment on the changes by death, of the vegetative Plankton (diatoms) in the organs of drowned bodies at winter, and has acquired the following results: 1) There were the 11 Diatoms were found in the water of the river used for this exepriment. 2) Most Diatoms were found in the lung and femur even two months after death but in the heart, liver and kidney in which each organs became softon, found the Diatoms only one month after death. Even after treating those organs, just a few Diatoms could be found. 3) Among 11 Diatoms, Cymbells parva, Melosira islandica and Cyclotella comta were considered in the strength for resisting to decomposition; and it was Tabellaria fenestrata which was not found at the earliest time.