10 PROTOPLASM AND PLANT CELLS 
results. Heat to 55° to 60° C. Now cool to about 30°. 
Examine again. 
(d) On similar specimens test the effect upon motion of 
iodine solution, alcohol, glycerine, ete. 
(e) Various types of protoplasmic 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. 
(f) 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 Ulothrix, 
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 lignified 
(wood) walls, yellowish brown. Stain another section with 
anilin-water safranin. This stains cutin walls yellowish and 
lignin walls bluish. 
(t) 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. 
(j) 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 little 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 
