THE CELL 19 



one or several large sap-cavities appear, the protoplasm 

 forming a thin layer closely appressed to the inner surface 

 of the cell-wall the cytoplasm. From this peripheral layer 

 of protoplasm thin strands or plates cross the cell from one 

 side to another. The turgidity of the cell, and the fact 

 that the protoplasm lies close to the inner surface of the 

 cell-wall, is due to the presence of the cell-sap, which, 

 according to the modern theory of solutions, explains that 

 substances in solution in water act like gases, and strive to 

 fly outwards or away from each other. 



Movements of protoplasm can be distinctly seen in 

 hanging-drop cultures, and according to Ternetz are neither 

 a circulation nor rotation, but a streaming. The current 

 passes easily through the cell-walls, or possibly through a 



jntral pore, and always maintains the same direction. Its 

 purpose appears to be the counteraction of differences of 

 turgor in different parts of the filament. 



On the other hand, Arthur observed that in certain 

 Mucors the currents of protoplasm are irregular and change 

 their direction, and are due to osmotic absorption of water 



some points of a filament, and to extravasation of water 

 at other points. 



Vacuoles are not simple cavities in the protoplasm, but 

 have a definite membrane according to Went, whose state- 

 ment is supported by other observers. De Vries has 

 shown by plasmolysis that the wall of the vacuole is an 

 osmotic membrane. 



The nucleus, as described by Wager in the basidia of 

 Agaricus muscarius and in A. stercoranus, agrees in 

 structure with that present in higher plants ; it possesses 

 a nuclear membrane, nucleolous, and nuclear network 

 made up of a thread coiled into a somewhat loose knot. 



