10 PROTOPLASM AND PLANT CELLS 



results. Heat to 55° to 60° C. Now cool to about 30°. 

 Examine again. 



{(I) On similar specimens test the effect upon motion of 

 iodine solution, alcohol, glycerine, etc. 



(e) Various types of proto])lasmic motion may be found in 

 the long cells of the young silk of Indian corn, in the cells of 

 the leaves of water weed (Philotria), the cells, especially those 

 near the ends of the shoots, of Chara or Nitella, etc. 



(/) To observe the different parts of a cell study again the 

 stem hairs of Petunia. Note nucleus, nucleolus cytoplasm, 

 vacuoles, cell wall. Cells from the leaf of a moss may also be 

 used for this purpose. 



(g) Bring into the laboratory some growing LTlothrix, 

 Cladophora, Stigeoclonium or other zoospore-producing algae, 

 and place in fresh water near the window. In a few hours one 

 can often find myriads of zoospores. Examine these for cells 

 lacking walls and provided with motile organs (flagella). 



(h) Make a thin cross-section of a herbaceous stem. Treat 

 with iodine solution and then with somewhat diluted sulphuric 

 acid. Cellulose walls are turned blue, cutinized and lignificd 

 (wood) walls, yellowish brown. Stain another section with 

 anilin-water safranin. This stains cutin walls yellowish and 

 lignin walls bluish. 



(i) Examine a thread of green felt (Vaucheria) or a vegeta- 

 tive thread of bread mold (Mucor) for a plant of coenocytic 

 structure. Note the lack of cross walls. The numerous 

 minute nuclei are not visible without staining. 



ij) The stone cells making up the shells of various nuts are 

 good objects to show the deposition of the cell wall in layers, 

 i.e. by apposition. With a pocket knife cut as thin a section as 

 possible, and place it in water containing a httle potash. At 

 the edges may be found areas thin enough for examination. 

 Here and there in the plainly layered cell wall will be found 

 pits, i.e. thin places left when the rest of the wall thickened. 



18. Plastids. Three kinds of plastids occur in plants. 

 They all agree in general structure in that they are denser 

 bodies of protoplasm imbedded in the cytoplasm. They 

 may have many shapes but are more frequently round or 

 elliptical in outline. So far as is certainly known new 



