280 



LEISURE-TIME STUDIES. 



has beheld, through the botanist's microscope, the move- 

 ments of the protoplasm in the cells (Fig. 48), of which 

 the hairs of Trades cant ia are composed, will not readily 

 forget the sight of the streams of protoplasm which hurry 

 hither and thither, laden with granules or solid particles, 



and which keep , up a 

 continual bustle within 

 the miniature world en- 

 compassed by the cell- 

 wall. The cells of the 

 stinging hairs of the nettle 

 afford an example of the 

 same wondrous spectacle. 

 " The protoplasmic layer 



FIG. 48. Cell of Tradescantia. The illus- of the nettle hair," SayS 



tration represents the same cell drawn at TT , , , 



successive intervals of two minutes, and MUXley, IS Seen tO DC 



showing alterations in the contained pro, in ^ condition Q f un _ 



ceasing activity. Local 



contractions of the whole thickness of its substance pass 

 slowly and gradually from point to point, and give rise to 

 the appearance of progressive waves, just as the bending of 

 successive stalks of corn by a breeze produces the apparent 

 billows of a corn-field." Thus the protoplasm of the plant- 

 cell is eminently active and contractile, and appears to be 

 the seat of energy as potent as that which animates and 

 directs the acts of an amoeba. 



But why, it may be asked, considering the presence of 

 sensitive protoplasm in plant-cells, do not we obtain the 

 same active responses from the plant when stimulated, that 

 we behold when the animal protoplasm is irritated ? The 

 answer is clear and apparent. Because the protoplasm of 

 the plant is not continuous. It is broken up into detached 

 portions separated by cell-walls, which present great, or it 

 may be insuperable, barriers to the transmission of impulses 

 through the plant-tissues. Each plant-cell, as regards its 

 irritability, is in fact an isolated unit ; and even in those 

 cases in which the plant becomes highly sensitive, as in 



