208 PliOTOPLASM. 



also more or less of the aggregation into rounded masses alluded 

 to in 564. 



575. The effect of mechanical irritation upon protoplasm in 



plants can be easily examined in cells or in plasmodia. When 

 a cell of Nitella which exhibits rapid circulation of protoplasm 

 is held somewhat firmly by pressure on the cover-glass, the 

 movement is arrested instantlv, but after a short time it is 



/ ' 



resumed. Even in those cases where the pressure has been 

 sufficient to disturb the arrangement of the chlorophyll granules, 

 the arrested motions are soon to be seen again. For experi- 

 ments upon the effect of pressure and shock, the stamen-hairs of 

 Tradescantia are even better than cells of Nitella or Chara, 

 for pressure brings about an apparent disintegration of the 

 threads, and all motion is suspended for several minutes ; but if 

 the injuiy has not been too severe, it soon begins again. How 

 far such injuries can be carried without affecting the vitality of 

 the protoplasm, may be seen from the following observations. 



According to Gozzi, 1 if a cell of Chara is ligated firmly, the 

 circulation is checked for a short time, and then begins in each 

 half of the cell. It is stated by Hofmeister that when a root- 

 hair of Hydrocharis Morsus-ranse is severed, the protoplasm in 

 the cell remains motionless for a short time, during which the 

 cut surface of the cell is being closed by a portion of the proto- 

 plasmic mass. When the surface is completely closed, the cir- 

 culation begins again within the healed cell. 



576. Rosanoff s observation, 2 which has been repeated many 

 times, is of much interest in connection with this subject. 

 When a cell from the endosperm of Ceratophyllum demersum, 

 having rapid circulation of protoplasm, is placed under the mi- 

 croscope, and a slight pressure is exerted on the cover-glass 

 for a moment, the circulation stops at once, the thick axile 

 threads of protoplasm begin to round at one or more places, and 

 from the aggregations slight processes, somewhat like tenta- 

 cles, appear. After a while these are retracted, and the normal 

 circulation is resumed. But sometimes it happens that these 

 tentacles become separated from the threads to which they be- 

 long, for a time lie without movement near them, and then 

 become again confluent with them. 



Mechanical shock 3 causes the active plasmodia of the myxo- 



1 Quoted ty Hofmeister in Die Lehre von der Pflanzenzelle, 1867, p. 50. 



2 Die Lehre von der Pflanzenzelle, p. 51. 



3 Hofmeister : Pflanzenzelle, p. 26. 



