14 



BOTANY 



PART I 



the boundary layer of the protoplasm take part in the movement. 

 Circulation is common in cells of land-plants, while rotation is more 

 usual in water-plants. 



When the protoplasm is in rotation, the cell nucleus and chromatophores are 

 usually carried along by the current, but the chromatophores may remain in the 

 boundary layer, and thus not undergo movement. This 

 is the case with the Stoneworts (Characeae), whose long 

 internodal cells, especially in the genus Nitella, afford 

 good examples of well-marked rotation. A particularly 

 favourable object for the study of protoplasm in circu- 

 lation is afforded by the staminal hairs of Tradescantia 

 virginica. In each cell (Fig. 5) currents of protoplasm 

 flow in different directions in the peripheral cytoplasmic 

 layer, as well as in the cytoplasmic threads, which traverse 

 the sap cavity. These cytoplasmic threads gradually change 

 their form and structure, and may thus alter the position of 

 the cell nucleus. 



Movements in limited regions of protoplasts are seen 

 in many of the lower Algae, especially in their swarm-spores. 

 Near the anterior end of the swarm-spore the protoplasm 

 may contain one or several minute pulsating vacuoles which 

 appear and disappear rhythmically at short intervals. They 

 empty suddenly, then reappear and slowly increase to their 

 full size (Fig. 333, 1 v). The protoplast of the swarm-spore 

 also possesses one or a number of threadlike contractile pro- 

 cesses (cilia, flagella) which vibrate rapidly and serve as the 

 motile organs of the cell. 



Only within a narrow range of temperature 

 is the protoplast actively alive, though life is 

 preserved through a slightly more extended range. 

 It dies and coagulates, as a rule, at temperatures 

 slightly above 50 C. Alcohol, acids of suitable 

 concentration, solution of mercuric chloride, etc., 

 rapidly coagulate the protoplasm, and such substances are largely 

 employed as fixing reagents in microscopical technique ( 7 ). 



FIG. 5. Cell from a 

 staminal hair of Tra- 

 descnntia viTginica, 

 showing the nucleus 

 suspended by proto- 

 plasmic strands. ( x 

 240. After STRAS- 



BURGEB.) 



C. Chemical Properties of the Protoplast ( 8 ) 



Active protoplasm generally gives an alkaline, under certain con- 

 ditions a neutral reaction, but never an acid one. It is not a simple 

 substance chemically, but consists of a mixture of a large number of 

 chemical compounds. Some of these undergo continual changes, upon 

 which undoubtedly many important manifestations of the life of the 

 protoplast depend. The most important components of the mixture 

 are the proteids. The protoplasm thus shows the reactions of proteids, 

 and when incinerated gives off fumes of ammonia. A whole series of 

 proteids occur in the living protoplasm. In the nuclei proteids contain- 



