PART III. 

 HISTOLOGICAL DEMONSTRATIONS. 



62. Granules and Brownian Movement. (H.) Rub 

 a piece of gamboge in a drop of water on a slide until the 

 fluid is faintly tinged ; cover, and examine. The term 

 fine granule is applied to a minute particle of any shape 

 that has no light centre. The term coarse granule is ap- 

 plied to a particle of irregular shape having a light centre 

 surrounded by a dark border. The difference between the 

 optical characters of the former and those of the latter is 

 entirely owing to size. Brownian motion is exhibited by 

 all minute particles floating in a fluid. The motion is pro- 

 bably owing to thermal currents in the fluid ; the solid par- 

 ticles merely indicating the directions of these currents. 



63. Hairs of Stamens of Tradescantia.* a. With 

 a pair of sharp-pointed forceps pull off a few hairs from a 

 stamen of a flower (a white flower if possible) that is just 

 opening. Place them in a drop of water on a slide ; cover, 

 and examine. 



(L.) The hair is a chain of cells rounded at its apex, 

 elongated towards its base. The youngest cell is at the 

 apex. 



(H.) Observe the envelopes, protoplasm, and nucleus of 

 each cell. In the youngest cells the protoplasm fills the 

 whole cavity. In the elongated cells there are irregular 

 spaces (vacuoles) in the protoplasm, between which it 

 stretches in the form of threads across the cavity of the 

 cell, towards the nucleus. It also forms a more or less 

 complete layer (primordial utricle) inside the envelope. 

 The protoplasm is a colourless finely granular jelly. Ob- 



* The Tradescantia Virginica is in flower from the middle of June 

 until the middle of October. 



