470 NATURE STUDY AND LIFE 



resulted in greatly impaired fruit, from lack of cross-polli- 

 nation, and apparently little difference in the distribution 

 of the blight. Affected limbs should be cut off a foot 

 below any traces of the blight and promptly burned. 



Foul Brood. — Large numbers of young bees are sometimes 

 found dead in the cells. This may be due to chilling, 

 but if the larva; have turned dark brown and softened to 

 the consistency of ropy mucus, and if the hive smells like 

 a glue pot, we have to do with the most fatal malady that 

 can attack a colony of bees. The disease is caused by 

 bacteria, and an affected hive may be the means of killing 

 all the bees in the neighborhood. California, Colorado, 

 Michigan, Nebraska, New York, Utah, Wisconsin, and 

 Ontario, Canada, have passed laws relative to foul brood, 

 which should be studied in connection with the lessons on 

 the honeybee. 



Symbiotic Bacteria. — Have members of the class prepare 

 a demonstration of the nodules found on the roots of 

 clover or peas. These are filled with bacteria, which we 

 here find in the new role of helpers and food producers 

 for the plant and for man. If time permits, we may try a 

 most instructive experiment. Wash thoroughly and ster- 

 ilize two flowerpots full of sand. Sow clover or peas in 

 both alike, except that the seeds for one pot should be 

 thoroughly washed with boiled water and soap, and those 

 for the other moistened with water in which root nodules 

 have been crushed. Let the plants stand side by side, 

 sprinkle with boiled or distilled water, and watch the dif- 

 ference in growth. Plants in the one pot can use only 

 the food stored in the seed ; those in the other will grow 

 with the aid of their symbiotic bacteria by receiving 

 nitrogen from the air. 



