APPENDIX 

 SPIROGYRA CELLS 



Filamentous algae have probably less right to being 

 considered as unicellular organisms than have 

 metazoan egg cells. But at least two studies of funda- 

 mental importance have been carried out upon Spiro- 

 gyra, of a kind which needs to be done upon ciliates 

 and bacteria. The first is that of Gerassimow upon 

 the dimensions of polyploid cells; the second is that of 

 VanWisselingh upon the accuracy with which cells 

 divide into equally-sized daughters. 



Spirogyra cells are contrasted with most protista 

 primarily by the presence in them of cell sap. Each 

 cell has a large mass of discrete material, which 

 is morphologically not a part of the cytoplasm; it oc- 

 cupies the core of the cell, leaving the cytoplasm as a 

 shell spread on the inside of the cell wall. The sap or 

 vacuole enlarges the cell's volume and surface, repre- 

 senting a saving, perhaps, of an equal bulk of metaboli- 

 zing materials. It is quite impossible to measure the 

 sizes of cells apart from the sap; indeed, the volume of 

 the sap is carefully regulated by the cells. 



Growth. Spirogyra lives in fresh-water as filaments 

 of cylindrical cells which are joined end to end. All 

 the cells of one thread are usually derived from a single 

 parent cell which may or may not have been a sexual 

 zygote. The diameter of a given thread is fairly uni- 

 form throughout its length, and is constant from one 

 day to another, so that the rate of growth in bulk can 

 be studied with fair accuracy by merely measuring the 

 lengths of filaments or cells from time to time. 



Spirogyra filaments were measured by Hofmeister 



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