NUCLEAR AND CELL DIVISION 81 



64. Cilculation of protoplasm in the cell. Use Elodea, or Nitella, or stamen 

 hairs of Tradescantia. 



A. Mount young leaves of Modea in water. Examine the simple cell 

 structure and find a favorable region for detailed study. 



1. Note the position and form of the chloroplasts, the nucleus, the cyto- 

 plasm, comparing with previous studies on plant cells. 



2. Study the circulation of protoplasm next the wall of the cell. Tocus 

 on a ohloroplast as it moves along, trace its path in a simple sketch 

 or diagram, and determine how long it takes to travel a certain 

 distance measured with the micrometer. Warm the slide gently. 

 What is the effect upon the rate of movement ? Describe the 

 movement carefully. Is the direction the same in all cells ? Does 

 the substance of the plasma membrane move, or is it granular 

 cytoplasm under the membrane ? 



B. Mount a portion of the stem of Nitella, including uninjured internodal 

 cells. Note the line called the neutral zone, free from chloroplasts, 

 which runs diagonally across the cell. The protoplasm on either side 

 of this line moves in opposite directions (see Principles, Sec. 230). 



C. Cut the stamens out of an opening flower or large bud of Tradescantia 

 and mount in water. The stamen hairs are chains of large and very 

 beautiful cells in which the nucleus and arrangement of the cytoplasm 

 may be seen with especial clearness. Are there chloroplasts present ? 

 What gives the peculiar reddish violet color to the cell ? 



Draw a cell on a large scale under h.p. and show the position of the 

 nucleus, and the moving streams of protoplasm, and indicate the 

 directions of the flow by arrows. 



65. Nuclesir and cell division in the root tip of an onion or other region of 

 growth (App. 8). The details of nuclear structure and nuclear division, 

 called mitosis, can only be studied in material carefully killed and hardened 

 to preserve the soft protoplasm as nearly as possible in its normal condition. 

 Thin sections must be cut with an instrument called the microtome and these 

 stained to differentiate the protoplasmic structure (Sec. 211). One of the 

 best stains is a combination of safranin (red) and gentian violet (blue). 



A. Examine sections under l.p. to determine the relation of regions or 

 tissues, and diagram the position of the root cap, the undifferentiated 

 embryonic tissue at the growing point, and the beginnings of the differ- 

 entiation which appears back of the growing point. 



B. Select a typical well-stained cell in the resting condition. Draw under 

 •h.p. and note : 



1. The nucleus with one or more deeply stained globules, each of which 

 is a nucleolus, or nucleole; a loose network containing chromatin; 

 the nuclear membrane ; the nuclear cavity which contains nuclear sap. 



