58 BOTANY part i 



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

 the physical })roperties of fluids, and on being artificially freed from 

 the cell wall, tends to assume the splierical 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 (Fig. 58). 



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

 enclosed bj'^ 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 (plasmoderma) 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 be Vries has applied the name 

 TONOPLAST to this layer. 



The small granules distributed through the granular plasma 

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

 SOMES. 



Even though bounded by a cell wall the cytoplasm frequently 

 exhi])its movements comjjarable to those of the naked amoebae and 

 Plasmodia of Myxomycetes. 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 Avidespread 

 occurrence in vegetable protoplasts ; the principle of this method 

 depends on the use of reflected light, and its dispei'sion by particles 

 that are so small as not to be visible on ordinary microscopic examina- 

 tion. 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 Avhich their power of creeping 

 a1)out is due, and finally a streaming movement in the cytoplasm. 

 The cytoplasm, enclosed b}^ a cell-wall, may either exhibit isolated 

 streaming movements, the direction of which may undergo re\'ersals, 

 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 circulation, on the other hand, the move- 

 ment is found both in the layer lining the cell wall and in the strands 

 traversing the vacuole. In no case does the boundary layer of the 

 jtrotoplasm take part in the movement. Circulation is common in 

 cells of land-plants, while rotation is more usual in water-plants. 



