228 GARDENS AND THEIR MEANING 



XI. Study of Bacteria 



Materials. Three test tubes, cotton, boiled potato, fruit or apple 

 sauce, three apples, one partly decayed. 



Directions, (a) Fill each tube about one third full of apple sauce. 

 Plug each with cotton. Set one aside. Put the other two into a 

 pail of water and boil for half an hour. After boiling, set one tube 

 aside with the cotton undisturbed. Take the cotton from the third 

 tube and leave it out for half an hour or more, then put it in again. 

 Leave these for a few days, note what happens and account for 

 different results. In canning fruit, is it desirable to leave the fruit 

 uncovered for a few minutes after cooking ? Why ? 



(b) Prick one of the sound apples in several places with a pin. 

 Put the pin into the rotten apple and then into the other sound 

 apple. Repeat this in several places. Set the two sound apples 

 aside for about a week. Note what happens and account for the 

 different results. 



NOTES ON SOILS 



I. Soil Materials 



Gravel. Coarse rock fragments. 



Sand. Corresponding in size to grains of sugar. 



Silt. Fine soil particles, smooth texture (for example, silicon for 

 cleaning knives). 



Clay. The finest rock particles. 



Humus. Decaying vegetable and animal substances (for ex- 

 ample, decaying leaves and twigs). 



II. Soil Variations 



Sandy soil. A mixture of sand and small amounts of silt, clay, 

 and humus, usually poor in nitrogen. 



Loam soil. A mixture of one half sand with clay and humus. 

 Fine, sticky. Good for general farming. The more humus the 

 richer in nitrogen, 



