A. Fleming: The material of the nucleus stained by basic dyes was given the name chromatin by Flemming . B. Robert Brown: The nucleus as a cell organelle was first described by Robert Brown , . C. George Palade: Ribosomes were first observed under the electron microscope as dense particles by George Palade . D. Camillo Golgi: Observed densely stained reticular structures near the nucleus, consisting of disc-shaped sacs or cisternae .