254 Introduction to Botany. 



which again form plasmodia under proper conditions of 

 humidity, etc. Such dry masses may be incited to resume 

 their active creeping stage by being kept between moist 

 felt paper under a bell jar. 



OBSERVATIONS. 



Bacteria and Yeasts. 



145. Put hay, cabbage leaves, or beans to soak in a 

 beaker of water, and leave the infusion standing in a warm 

 place until the liquid becomes cloudy. Then examine a 

 drop under a high power ; minute bodies of various forms 

 will be seen, some of them in rapid motion. The smaller 

 rounded, rod-shaped, or corkscrew-shaped bodies are bac- 

 teria, the smallest known plants. 



146. Boil a potato and cut it in two with a knife which 

 has been sterilized by baking in an oven. Dip into the 

 above infusion the point of a needle which has been steril- 

 ized in the flame of an alcohol lamp or Bunsen burner, 

 and then lightly make a few scratches with the point of 

 the needle across the full length of the cut surface of the 

 potato. Put the inoculated potato under a bell jar or other 

 dish, together with some moistened filter paper to keep the 

 potato from becoming dry. Examine the preparation from 

 day to day. Mount under a coverglass some of the 

 growths which appear, and examine with a high power. 

 Doubtless growths will appear on the potato outside the 

 scratches, because not enough care has been taken to 

 exclude the possibility of accidental inoculation ; but the 

 growths along the scratches will be sufficiently definite for 

 our present purpose. 



The experiment might be varied by touching one half of 

 the potato against some dusty place in the room, and 



