134 The Phenomena of Morphogenesis 



enough to pull them away from the walls and break whatever connec- 

 tions there may have been with other cells, but without killing them. 

 The plant was then deplasmolyzed. Each cell, now as effectively isolated 

 as though it had actually been removed, began to enlarge, broke out of 

 its wall, and proceeded to regenerate a new filament. The significant 

 fact is that from the basal end of each cell a new rhizoid was formed 

 and from the apical end, a new thallus. The polar character of the cells, 

 otherwise impossible to demonstrate, could thus be established. These 

 experiments were repeated and extended by Czaja (1930; Fig. 6-12). 

 Borowikow (1914) succeeded in reversing the polarity of Cladophora 



Fig. 6-12. Polarity in a single cell. 

 A cell isolated from a filament of 

 Cladophora, regenerating a thallus 

 from its apical end and a, rhizoid 

 from its basal one. (From Czaja.) 



cells by centrifugation, showing again the close relation between the 

 distribution of material in the cytoplasm and the polarity of the cell. 



In some filamentous algae, the plant's organization may disintegrate 

 under certain circumstances and the individual cells thus become freed 

 from their correlative inhibition. In Griffithsia, for example, Tobler 

 ( 1904 ) observed such cells in culture and found that, when they began 

 to regenerate, rhizoids grew from the basal end (distinguishable by its 

 shape) and shoots from the apical one. Schechter (1935) centrifuged 

 similar ones and found that their polaritv could be altered by this means 

 and that shoots always appeared at the centrifugal pole. 



The rather loosely organized tissues of these simple algae provide ex- 

 cellent material for studies in cellular polarity even though their cells 



