354 The Microscope. 



the bulb. We will cut through these outer layers in a radial 

 direction with a sharp knife (for we will find it sensitive to 

 wounds), in the form of a little square, half inch on a side, and 

 remove the piece cut through, just as the boy plugs a water- 

 melon, in his neighbor's melon patch. On the inside of this 

 leaf-piece, or on the outside of the next, we find our film in good 

 form to handle and to mount, and we carefully transfer it to a 

 drop of water on a slide, and another drop on the cover glass 

 will insure the mount to be free of air bubbles ; it is all impor- 

 tant that our section be taken from an onion that is growing 

 and otherwise healthy, as we learn further along ; this we have 

 tried to do ; it has a new green shoot more than an inch long, 

 and we see no mould on it. I can hardly hope to give such defi- 

 nite directions as may enable others at sight to select the best 

 onions for this work, for I have had much trouble to find them 

 myself. A solid, plump little onion set, although beginning to 

 shoot, did not afford my best specimens ; large healthy onions, 

 as gathered in Autumn from the field, and not yet shooting at 

 all, were hardl}'- to be considered very good ; in both of these 

 the protoplasm was very dimly seen. It was among the grow- 

 ing onions that were somewhat softened, yet not too much dried, 

 that I found my best working material ; these gave me the rich- 

 est, best' flowing and most conspicuous protoplasm ; when the 

 bulbs had wilted and dried, so that the films were adherent, they 

 were useless, and worse when grayish. The film should separate 

 easily and come off freely with a clear, watery appearance, to 

 give pny promise of usefulness ; even then something may be 

 wrong, and it fails us. 



My experience with mould on the onion, even in small patches, 

 was unfavorable ; a section with but a few twigs of mycelium in 

 one corner was worthless; the mould, in some way, either by 

 shock from the injury it was doing or by poisoning, had killed 

 the protoplasm in all the cells of the entire section. With a 

 low or medium eye piece at the top of our tube (I prefer a " C " 

 periscopic and a low powe'" objective, say a half inch), we find 

 our specimen made up of a single sheet of cells, that is, but one 

 cell deep and joined together at the ends and sides by partition 

 walls, a most admirable arrangement given us by nature for this 

 study; no cut section can imitate it. The cells are very large; 

 can be seen by the naked eye to be from half to three quarters 



