the immediate principle of vegetable and animal life. This discovery is one of the most important results of research in modern natural science. Not less important were the results obtained from the study of the rest of the organised contents of cells; von Mohl proved that chlorophyll-corpuscles, the most considerable organs of nutrition in the plant, are formed of protoplasm, and Theodor Hartig, though his cell-theory was a mistake, did good service by his discovery of aleurone-grains in seeds and of the crystalloids which sometimes occur in the grains, and which are also formed of protoplasm and renewed from protoplasm. Radikofer, Nägeli, and others added to our knowledge of the form and chemical composition of these aleurone-grains. To starch-grains, which had been frequently examined, by Payen especially, Nägeli devoted an investigation at once comprehensive and profound, and obtained results of extraordinary value; these were given to the world in an exhaustive work published in 1858 under the title ‘Die Stärkekörner,’ and form an epoch not in phytotomy only, but in the general knowledge of organised bodies. By the application of methods of research unknown before in microscopy, Nägeli arrived at clear ideas of the molecular structure of the grains, and of their growth by the introduction of new molecules between the old ones. This theory of intussusception founded on the observation of starch-grains derives its great importance from the fact that it served directly to explain the growth of cell-membrane, could be applied generally to molecular processes in the formation and alteration of organic structures, and accounted for a long series of remarkable phenomena, especially the behaviour of organised bodies in polarised light. Nägeli’s molecular theory is the first successful attempt to apply mechanico-physical considerations to the explanation of the phenomena of organic life.