324 THE CELL 



done to its vital functions, it soon develops upon its surface a new 

 cellulose layer, which becomes stained red when congo-red is 

 added to the water. 



As long as cells are young and growing vigorously, they contain 

 a large quantity of protoplasm, whilst older cells, especially those 

 in which formative activity has been arrested, only contain a small 

 quantity of it. For instance, the protoplasmic layer, on the inner- 

 surface of the cellulose membrane of large and fully developed 

 plant cells, may be so extremely thin that its presence, as a dis- 

 tinct stratum, can only be demonstrated by means of plasmolysis. 

 Similarly, only minute traces of protoplasm are present in the 

 notochordal cells of animals, etc. 



The relations that the nucleus bears to the remaining com- 

 ponent parts of the cell are at present attracting great attention. 

 It has already been shown (p. 214) that very remarkable meta- 

 bolic interactions take place between the nucleus and the proto- 

 plasm during the processes of division. But it is evident, that 

 the nucleus plays an important physiological part at other times, 

 as well, in the life of the cell ; all the formative and nutritive 

 processes seem to be dependent upon it, and to bear a close re- 

 lationship to it. The true nature of this relationship, however, 

 cannot at present be more exactly defined, as may be deduced 

 from the observations of Haberlandt and Korschelt, which will be 

 described later, as well as from the experiments of Gruber, Nuss- 

 baum, Balbiani, Klebs and Hofer. 



I. Observations on the position of the nucleus, as an 

 indication of its participation in formative and nutritive 

 processes. According to the extensive and important observa- 

 tions of Haberlandt (VIII. 4) the nucleus of young and developing 

 plant-cells is " situated in that portion of the cell where growth is 

 most active, or lasts longest. This is true both for the growth of 

 the cell as a whole and for the increase in volume and superficial 

 area of the cell-membrane in especial. If the cell is growing in 

 more than one place, the nucleus takes up a central position, so 

 that it is about equidistant from the regions of most active growth 

 (Fig. 161, II). Occasionally the nuclei are connected with the 

 places of most active growth by means of protoplasmic strands, 

 which are as short as possible. The nucleus only rarely retains 

 its original position in fully developed cells. As a rule it has left 

 the place which it occupied in the growing cell, and generally has 



