DIV. I 



MORPHOLOGY 



13 



B. Main Vital Phenomena of Protoplasts 



In order to facilitate an insight into the real character of proto- 

 plasm, attention will first be directed to the SLIME FUNGI (Myxo- 

 mycetes), a group of organisms which stand on the border between the 

 animal and vegetable kingdoms. The Myxomycetes are characterised 

 at one stage of their development by the formation of a PLASMODIUM, 

 a large, naked mass of protoplasm (Fig. 4). The cytoplasm consists of 

 a clear ground substance, through which granules are distributed. 

 This substance is of the consistence of a tenacious fluid; its superficial 

 region is denser and free from granules, while these are numerous in 

 the less dense central portion. The granules enable the internal 

 streaming movements of the cytoplasm to be recognised. The 

 currents are constantly changing 

 their direction, moving either 

 towards or away from the margin. 

 The formation and withdrawal of 

 processes of the margin stand in 

 relation to the direction of the 

 currents. When naked masses of 

 protoplasm such as these plas- 

 modia encounter foreign bodies, 

 they can enclose them in vacuoles, 

 and, when of use as food, digest 

 them. 



Even though bounded by a 

 cell wall the cytoplasm frequently 

 exhibits movements comparable to 

 those of the naked amoebae and 

 plasmodia of Myxomycetes. These 



movements are usually found in somewhat old cells. The stimulus 

 caused by wounding the tissues in making the preparation frequently 

 increases the activity of the movement ( 6 ) ; apparently it quickens 

 the transport of nutrient material toward the wound. Such move- 

 ments show that here also the protoplasm is of the nature of a 

 tenacious fluid. When freed from the cell wall it assumes the form of 

 a spherical drop. 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 CIR- 

 CULATION 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 movement is found both in the layer lining the 

 cell wall and in the strands traversing the vacuole. In no case does 





BURGER.) 



