118 VEGETABLE CELLS. 



depends either on the share which the parent-cell bears in 

 the production of the secondary cells, or on the physiolo- 

 gical similarity or dissimilarity which exist between the 

 parent-cell and the secondary cells. In reference to the 

 first point, it is of importance whether the whole contents 

 of the parent-cell, or only larger or smaller portions of the 

 contents, are converted into secondary cells, and in what 

 number these are produced in the parent-cell. In refer- 

 ence to the second point, either perfectly similar or dis- 

 similar secondary cells may be formed in the parent-cell. 

 Physiologically similar secondary cells are produced in 

 Hcematococcus and Chlorococcus ; all other cells originating 

 through free cell-formation, are more or less different in 

 physiological respects from the parent-cell. 



The question still remains, to what extent is free cell- 

 formation met with in the vegetable kingdom ? In the 

 first part of this essay,* I limited parietal cell-formation 

 to several families of Algae, and the special parent-cells 

 of the four-spored Cryptogamia and the Phanerogamia. 

 For all the examples there enumerated, I had observations 

 which more or less bore out the statement. Free cell- 

 formation, on the other hand, I was acquainted with in 

 the endosperm-cells and in the germ-cells of Algae, Fungi, 

 and Lichens. For all other cases, especially for all vege- 

 tative cells of four-spored Cryptogamia and the Phane- 

 rogamia, the decision depended partly on analogy, partly 

 on some observations of Schleiden's, and of my own. I 

 therefore concluded : In parietal cell-formation the nu- 

 cleus is, as a rule, central ; in the free cell-formation in 

 the embryo sac, the nucleus is lateral. It is probable from 

 this, since the cells of the higher Cryptogamia and the 

 Phanerogamia possess a lateral nucleus, that they origi- 

 nate by free cell-formation. The secondary cells were, 

 moreover, figured actually free within the parent-cell, in 

 certain cases, by Schleiden and by myself. I was satisfied, 

 therefore, that the cells with lateral nuclei originated free. 



Observation and reflection have since led me to a 



* Ray Trans., p. 292. 



