CELL-FORMATION . 117 



at a very early period. In the germ-cells, the nuclei are 

 distinct, as such, sometimes never, sometimes only in the 

 fully-developed condition of the cell. Since the nuclei 

 can be distinguished sufficiently early in the endosperm- 

 cells, it is also possible to observe their relation to cell- 

 formation. Since the nuclei of the germ-cells cannot be 

 distinguished until a late period, their relation to cell- 

 formation cannot be made out by direct observation. This 

 is the more conceivable, that the endosperm -cells are many 

 times larger than the germ-cells, and their nuclei than 

 nuclei of the latter. Besides this, endosperm-cells do also 

 occur in which the presence of a nucleus, and its coopera- 

 tion in the cell-formation, cannot be distinctly seen. This 

 is especially the case when the contents of the nucleus 

 and those of the young cell are homogeneous and of equal 

 density. What I have stated is, I think, sufficient reason 

 why the apparent want of nuclei in the free formation of 

 germ-cells cannot be maintained as a proof of an actual 

 absence of these bodies. 



Normal free cell-formation thus comprehends, according 

 to my views, the following essential and regular periods : 

 A nucleus originates in the contents of the parent-cell. 

 This accumulates on its surface, by attraction, a greater 

 or smaller quantity of the contents of the parent-cell, 

 which, at least at the periphery, consist of homogeneous 

 mucilage. This portion of the contents becomes coated by 

 a membrane over its entire surface. 



The variations which occur within the limits of this 

 identity, refer either to the nature of the portions of con- 

 tents which become individualized, or the relation of the 

 secondary cells to the parent-cell. The portion of con- 

 tents which become isolated, exhibit chemical and mor- 

 phological variations. They are composed either of 

 homogeneous, colourless mucilage ; of homogeneous 

 colourless mucilage mingled with colouring matters; of 

 granular mucilage, or granular mucilage mixed with 

 colouring granules and starch-globules. 



The relation of the secondary cells to the parent-cell 



