58 BOTANY PART i 



a cell wall, is a more or less tenacious fluid. It partakes of the 

 physical properties of fluids, and on being artificially freed from the 

 cell wall, tends to assume the spherical form. Its cohesion appears 

 to be greater in meristematic cells than in those which are older, 

 while in certain cases a still firmer consistence may be attained as 

 in the cilia borne by swarm-spores. 



Both in the case of the Myxomycete and of the vegetable cell 

 enclosed by a wall, the basis of the cytoplasm consists of a hyaline 

 substance termed the HYALOPLASM. When granules are distributed 

 through the cytoplasm it is spoken of as GRANULAR PLASMA or polio- 

 plasm. An extremely thin boundary layer is found at the periphery 

 which is quite free from granules, and a similar layer bounds 

 every vacuole present in the cytoplasm. The wall of the vacuole 

 is characterised by a greater tenacity of life than the rest of the 

 cytoplasm, remaining alive for some time after the latter has been 

 killed by the action of a 10 per cent solution of potassium nitrate. 

 Since the vacuole- wall regulates the pressure exerted by the cell 

 sap contained in the vacuole, HUGO DE VRIES has applied the name 

 TONOPLAST (M) to this layer. 



The small granules distributed through the granular plasma 

 consist of various substances, and may be classed together as MICRO- 

 SOMES. Some of them are small cavities filled with dissolved 

 substances, and to these the name PHYSODES has been given. 



Even though bounded by a cell wall the cytoplasm frequently 

 exhibits movements comparable to those of the naked amoebae and 

 plasmodia of Myxonwcetes. These movements mostly are found in 

 somewhat old cells, but N. GAIDUKOV (^ has shown by means of 

 the recently invented ultramicroscope that they are of widespread 

 occurrence in vegetable protoplasts. The study of the movements 

 in the Myxomycetes showed that various kinds of movements could 

 be distinguished ; the waving movement of the flagellum of the 

 swarm-spore, the change in external form of amoebae and plasmodia, 

 to which their power of creeping about is due, and finally a streaming 

 movement in the cytoplasm. The cytoplasm, enclosed by a cell- 

 wall, may either exhibit isolated streaming movements, the direction 

 of which may undergo reversals, or a single stream, the direction of 

 which is constant. These two forms of movement are distinguished 

 as CIRCULATION and ROTATION respectively. In rotation, which is 

 found in cells with the cytoplasm reduced to a layer lining the 

 wall, the single continuous current follows the cell wall. In circula- 

 tion, on the other hand, the layer of cytoplasm lining the wall takes 

 no part in the movement, which is found in the strands traversing 

 the vacuole. Circulation is common in cells of land-plants, while 

 rotation is more usual in water-plants. The stimulus caused by 

 wounding the tissues in making the preparation frequently increases 

 the activity of the movement ( 35 ). 



