DIVISION OF THE VEGETABLE CELL. 31 



which was; that there is, in the first instance, a structureless sub- 

 stance present, sometimes fluid, sometimes more or less gelatinous. 

 This substance possessed within itself power to occasion the pro- 

 duction of cells. When this took place, the nucleus usually ap- 

 peared first, and then the cell was formed around it. The sub- 

 stance in which the cells arose was named cell-germinating mate- 

 rial, or cytoblastema. 



This process was known as free cell-formation, and until quite 

 recently was believed to be the one by which the first endosperm 

 cells were produced within the embryo-sac of flowering plants. 

 Such, however, Strasburger — who has for ever linked his name 

 with the life-history of cells — has proved not to be tlie case, and 

 that they, in common with all others, are derived from tlie division 

 of pre-existing nuclei and cells. 



In but few, if any, departments of biological science, has greater 

 advance in knowledge been made during the last five years than 

 has taken place with regard to the structure and division of nuclei. 

 Essentially protoplasmic in its nature, it was believed to be devoid 

 of structure, but denser and more highly refractive than the proto- 

 plasm in which it is enclosed. But during the last few years, owing 

 to the labours of many observers, but notably Strasburger and 

 Flemming in Germany, and Klein in England, the views pre- 

 viously held have been completely revolutionized. 



Nuclei are now known to consist of two elements, differing 

 from each other chemically as well as in appearance. The one 

 is dense, the other is semi-fluid, the denser one being also more 

 highly refractive. The first names proposed for them were nuclear- 

 fluid and nuclear- substance respectively; but seeing that the one 

 was in reality never a true fluid, another and more satisfactory 

 nomenclature has been proposed. The best results — so far as the 

 observation of the structure and behaviour of nuclei in vegetable 

 cells are concerned — are obtained in tissues whose protoplasm has 

 been fixed by means of absolute alcohol, and the sections stained 

 with Hematoxylin ; and in preparations so treated it is found that 

 the nuclei are most beautifully stained, while all else either 

 remains uncoloured or is tinted to a very small extent. And 

 further it is found that in nuclei either preparing for or in 

 process of division, only one of the elements is coloured, the 

 other remaining colourless, the denser substance taking the stain 

 intensely, the other refusing it. Here we have at least an indica- 



