262 CRYPTOGAMS 



225. BACTERIA 



Object. To demonstrate the relation between soil bac- 

 teria and the growth of plants. 

 Apparatus. Flowerpots, soil, clover seed or alfalfa. 



Method. Fill two flowerpots of medium size with soil. 

 Rich soil dug from a field where clover is growing is the 

 best for the purpose. Sift the soil to remove stones, roots, 

 and other coarse matter. 



Heat one flowerpot in an oven for an hour. This will 

 sterilize the soil if the heating has been thorough. 



Sterilize seeds of clover or alfalfa by rinsing them in a 

 very dilute solution (2 per cent) of formalin and then rinse 

 them in distilled or sterilized water. 



Plant the sterilized seeds placing an equal number in each 

 of the flowerpots. 



The seeds will then be placed in exactly similar conditions 

 with exception of the soil which in one flowerpot has been 

 freed of bacteria, while the other has not been sterilized. 



Place both pots under conditions favorable for growth and 

 keep them so until the young plants have been growing for 

 some time. 



What difference is noticed in the two plants? Compare 

 them as to height, vigor, number of leaves, and general 

 appearance. Keep the plants growing if necessary for a 

 month or six weeks before making the comparison. Remove 

 both plants from the soil by turning the flowerpots over so 

 that the roots will come out uninjured, and examine the 

 exposed roots. Are they alike? If not, what differences 

 are observable? Draw or make blueprints of the root of 

 each plant. 



Conclusion. What may be inferred as the difference 



