If a drop of strong solution of potassium bichromate, placed upon a microscope-slide, be observed under the microscope as it crystallizes, and if the drop be sufficiently thin, it will generally be found that the following events take place: The first crystals make their appearance at the edges of the drop and after growing rapidly for a short period as branching fibres, they begin to grow quietly in the form of plates or flattened rods presenting the characteristic form of the crystals of this substance. These crystals continue to grow uniformly, but after a short period, at a distance from the growing crystals, and at some spot where the drop is thin, a fresh crystalline growth starts suddenly from a point, and extends with great rapidity in all directions in the form again of branching needles and fibres.