66 THE MICROSCOPE AND CELL-STRUCTURE. 



(6) With the high power notice (1) the smooth, colourless cell- wall ; 

 (2) the thin film of granular protoplasm immediately within the cell- 

 wall, in which are embedded (3) the flat green bauds, which have 

 ragged edges, and show at intervals small rounded highly refractive 

 bodies, the pyrenoids ; (4) the large central cavity (vacuole) of the cell, 

 containing colourless transparent cell-sap ; and (5) the highly refrac- 

 tive spherical or lens-shaped nucleus in centre of cell. 



(c) Stain some filaments with iodine, and observe that the pyrenoids 

 have become dark purple or almost black, owing to the presence of 

 crowded small starch-grains, and that the nucleus is connected with 

 the outer layer of protoplasm by fine threads, each usually ending at a 

 pyrenoid. 



(d) Mount some Spirogyra filaments in water, place at one edge of 

 the cover-glass a few drops of salt-solution, and while watching a 

 filament, draw the solution under the cover-glass by holding a piece of 

 blotting-paper at the other side. Notice that the protoplasm shrinks 

 from the cell-wall, as water passes by diffusion (osmosis) from the cell- 

 sap in the vacuole into the salt-solution outside. Sketch the contracted 

 or plasmolysed cell, then draw a little water under the cover in the 

 same manner, and notice the cell return to its normal turgid condition. 



(e) Place some Spirogyra filaments in alcohol, and after a day or 

 two notice that the spiral bands have become colourless, the green 

 colouring matter (chlorophyll) having been dissolved by the alcohol, 

 which also contracts or plasmolyses the cells. 



99. Other Simple Preparations. Many other interest- 

 ing and instructive preparations can be made by using fresh 

 materials simply mounted in water, e.g. leaves of Mosses, of 

 water-plants (Elodea, Nitella, etc.), roots of seedlings (note 

 the root-cap, root-hairs, rootlets). 



(a) Mount in water a few whole leaves of a thin-leaved Moss (try 

 several kinds and select those which show large and clear cells), or a 

 Fern prothallus. Note the polygonal cells, joined to form a plate, 

 without any spaces between them, and in each cell note the protoplasm, 

 the vacuole, the nucleus (seen especially well on staining with iodine 

 solution, which, however, kills the cell), and the numerous small disc- 

 like chloroplasts or chlorophyll-corpuscles (stained purple with iodine 

 if they contain starch). 



(6) In Moss cells you can see the chloroplasts in the act of dividing. 

 The chloroplast becomes lengthened and then nipped across the middle 

 so as to resemble a dumb-bell, eventually separating and forming two 

 chloroplasts. 



(c) Get some Canadian Waterweecl (Elodea), which grows abundantly 

 in many rivers and canals, having long submerged stems and leaves 

 arranged in threes at each " node." Mount a few leaves in water, and 

 look for the streaming movements of the protoplasm, which may be 



