330 THE CELL 



cell-wall. This does not prevent it from eventually fulfilling 

 other functions in the fully developed cell." (Haberlandt.) 



3. The nucleus takes part both in the excretion and absorp- 

 tion of material. This is shown by its position, and also by the 

 fact that the nucleus increases its superficial area by extending 

 numerous processes towards the place where excretion and absorp- 

 tion are occurring. 



II. Experiments proving the reciprocal action of the 

 nucleus and protoplasm. The experimental researches of 

 Gruber, Nussbaum, Hofer, Yerworn, Balbiani, and Klebs have 

 led to the same results. Their method was to divide by some 

 means or other, a unicellular organism or a single cell into two 

 portions, one nucleated and the other non-nucleated, and then to 

 follow and compare their future behaviour. 



By means of plasmolysis in 16 per cent, sugar solution, Klebs 

 was enabled (IV. 14 ; VIII. 7) to divide the cells of Spirogyra 

 threads into one nucleated part and several non-nucleated portions. 

 Although these latter sometimes live for six weeks before they 

 disintegrate, the vital processes occurring in them differ con- 

 siderably from those taking place in the nucleated ones, the latter 

 continuing to grow and to surround themselves with a new cell- wall, 

 which stains easily with congo red, and can thus be rendered 

 visible. The former on the other hand remain globular in form, 

 do not increase in size, and develop no cell- wall. That the 

 latter process is considerably influenced by the presence of the 

 nucleus, is clearly shown by the fact that, when the fragments 

 obtained by means of plasmolysis, are connected by a thin 

 bridge of protoplasm, the non-nucleated part is able to form 

 cellulose. 



However, certain metabolic processes take place in protoplasm 

 without the presence of the nucleus ; for instance, the non- 

 nucleated parts are still able to assimilate, to dissolve, and to form 

 starch, provided that they contain a portion of the chlorophyll- 

 band. If they are kept for a considerable time in the dark, they 

 become free from starch, because they have used up the stock of 

 stored-up granules; when they are brought back again into the 

 light, the chlorophyll bands recharge themselves with newly- 

 assimilated starch ; indeed, in this case the accumulation of starch 

 is even greater than in the nucleated part, probably because its 

 consumption, whilst all the other vital functions are in abeyance, 

 is reduced to a minimum. 



