FIFTH SECTION. 

 Movements of Irritation. 



I THE MOVEMENTS OF IRRITATION" OF PROTO- 

 PLASMIC STRUCTURES. 



168. Protoplasmic Movements. 



As the first object for examination, we take Nitella, an alga 

 which is fairly common in stagnant waters poor in lime, employ- 

 ing the younger internodes for microscopic observation. Without 

 going further here into the well-known peculiarities ^of the 

 elongated cells of Nitella, it may be remarked that the ectoplasm 

 (Hautschicht) or hyaloplasm is specially well developed in these 

 cells. This ectoplasm, and likewise the chlorophyll grains 

 embedded in it, are motionless ; in the granular layer, on the 

 contrary, very active movement can be perceived. We have here 

 to do with typical rotation, for the stream returns into itself. 

 The ascending part of the stream is separated from the descending 

 part by the indifferent strip. 



If we mount leaves from the bud of Elodea canadensis in a drop 

 of water, and examine under the microscope, we recognise without 

 any trouble the parietal layer of protoplasm, the protoplasmic 

 bands traversing the cell-sap, the nucleus, and the chlorophyll 

 grains. We also at once see that movements are taking place in the 

 protoplasm, which are readily observable owing to the change in 

 position which the chlorophyll grains undergo. The protoplasmic 

 movement in the cells of Elodea leaves is sometimes more of the 

 nature of rotation, sometimes more of the nature of circulation. 



In this latter the currents, which may occur both in the parietal 

 layer and in the protoplasmic bands, take the most various 

 directions ; often the currents in one and the same band even are 

 differently directed. Redistributions of mass take place in the 

 protoplasm ; some strands become thinner, others completely 



P.P. 417 E E 



