382 BOTANICAL GAZETTE [November 



coagulates (rapid or slow dissolution may follow as well as precede 

 coagulation). The coagulum is coarsely granular in appearance, 

 suggesting a granular precipitate. 



Brownian movement of protoplasmic particles 



It is rather surprising how little the presence of Brownian 

 movement of particles in really living protoplasm is appreciated. 

 It is usually said that protoplasm, because of its comparatively 

 high viscosity, will not permit Brownian movement of its particles, 

 and that only in vacuoles, whose contents is a dilute sap, is Brown- 



* 



ian movement of particles to be observed in a living cell. The 

 classical example of this is the terminal vacuoles of the desmid 

 Closterium. It must be borne in mind that I have reference here 

 only to microscopically visible particles, such as make up the 

 granular plasm, and not to ultramicroscopic colloidal particles 

 which are in a constant state of vibration in probably all liquid 

 protoplasm. When workers refer to ""the Brownian movement of 

 particles" (2) contained in protoplasm, they do not always explain 

 whether the reference is to microscopic or ultramicroscopic particles. 

 Usually it is apparently the latter. Brownian movement of sus- 

 pended microscopic particles in protoplasm cannot be seen in 

 by any means all cells or organisms, but it is to be observed in 

 the dilute endoplasm of some ciliates, in the liquid protoplasm of 

 streaming Myxomycetes, and to a striking degree in one of the 

 most studied of organisms, Amoeba. 



In a quiescent Amoeba the number of particles exhibiting 

 Brownian movement is small, and the amplitude of the movement 

 is short. In an active Amoeba^ the protoplasm of which is more 

 dilute, all particles except the largest droplets exhibit Brownian 

 movement, the motion varying inversely as the size of the particle 

 (4 /x seems to be the maximum size of particles capable of the 

 vibration, according to Yocom 30), and the amplitude of vibra- 

 tion is relatively large. In the liquid endoplasm of the ciliate 

 infusorian Euplotes the suspended particles are frequently in a 

 state of vibration, especially when cyclosis is taking place. 



The protoplasm of Amoeba in which Brownian movement is to 

 be observed is of rather liquid consistency, and when this proto- 



