322 Dr Martin Barry on 



the nucleus to have been — M absorbed." Nothing, as I have 

 shewn, could have been further from the truth. The nucleus 

 had exhausted itself in the formation of fibre for secondary 

 membranes (or other deposits) and division of the cell. 



Thus there occurs no folding inwards of a " primordial 

 utricle'' for division of the cell, as maintained by Von Mohl ; 

 nor does there take place for this purpose a division of the 

 contents of a parent cell into two parts, around which con- 

 tents are formed the walls of two young cells, as supposed 

 by N'ageli and Hofmeister.* 



Annular, Spiral, and other Fibrous Deposits in the Vessels of 

 Plants ; — their mode of Origin. 



Each of these I find to be originally a fibre of the twin spiral 

 form in question. Their mode of origin is therefore al- 

 most implied by what has just been said regarding the 

 nucleus of the cell. Thus, when the nucleus becomes a ring, 

 the deposit is annular ; when the nucleus becomes an inci- 

 pient coil, many of these unite end to end to form a long one ; 

 which sometimes remains single, and sometimes divides and 

 subdivides ; and if the divisions of such deposits, whether 

 annular or spiral, be not continued but partial and irregular, 

 we have the reticular form as well as an explanation of the 

 supposed tendency in vegetable fibre to anastomosis. 



Importance of the Nucleolus. 



The nucleolus is thus the essential part of both the " cyto- 

 blast" and nucleus. However inappreciable, it is never alto- 

 gether wanting. This nucleolus it is which, where cells are re- 

 producing cells, descends by fission from cell to cell. It is 

 the organ of absorption, assimilation, and secretion ; secret- 

 ing, for instance, the red colouring matter of the blood in the 

 outer part of the blood-disc. It is continually passing from 

 the state of nucleolus into that of nucleus ; continually giving 



* " Principles of the Anatomy and Physiology of the Vegetable Cell." By 

 Hugo von Mohl. Translated by Arthur Henfrey, F.K.S., pp. 50-57. 



