412 PROTOPLASM. PART n. 



of the structure of plants that according to the ob- 

 servations of Mr. Wenham, the difficulty is to find a 

 plant, aquatic or terrestrial, in which it does not take 

 place at some period of its growth. The gyration in 

 any given cell preserves a uniform direction ; in different 

 cells the direction is different. It will persist in a de- 

 tached part of a plant for several days or even several 

 weeks. It is arrested by cold, and recommences its 

 gyration when the temperature is raised. 



It has been mentioned that in the primordial cell the 

 solid coloured particles often form a nucleus in the 

 centre of the viscid liquid called protoplasm, which is 

 continually diminished by the increase of the watery 

 vegetable sap. At length the protoplasm in the hairs is 

 reduced to mere threads extending from the cell wall 

 to the nucleus, so that the latter looks like a spider in 

 the middle of its web. These threads are really streams 

 of the viscid protoplasm flowing through the more 

 liquid cell sap from the nucleus to the cell wall, where 

 they turn and flow back again in another thread. 

 When there are several currents in the same cell, the 

 nucleus, which is the common point of departure and 

 return, is the centre of the vital activity of the cell, 

 though it does not always maintain a central position ; 

 in the cells of the leaves of the Yallisneria spiralis the 

 nucleus even follows the protoplasm, which flows in a 

 broad stream up one side of the cell and down the other, 

 as in the Chara. In most plants the gyration is transi- 

 tory, for the nucleus which always exists in young cells 

 is dissolved as the cell advances in age, and the pro- 

 toplasm is so much diminished in quantity, that its 

 motion is imperceptible. There are exceptions, how- 

 ever, as in the hairs of the nettles and some other plants, 

 where it is persistent. 



The motion is in general very slow. The thinness and 

 minuteness of the currents may be imagined, since they 



