Growth. 29 



for a day. Remove the seeds, and place in a germinator under 

 temperatures at which the seeds ordinarily grow. Note the 

 number that have germinated at the end of a week. Put a 

 second lot of the same seeds in the incubator, and keep at 

 about 60° C. for a day, then test in germinator. Repeat both 



Fig. 14.— Zurich germinating.dishes standing in a glass disli in wliicli a con- 

 stant supply of water is kept by an inverted flask. 



tests, placing the seeds that are in the incubator in dishes of 

 water. Compare with results obtained from air-dry seeds. 



22. Effect of freezing temperatures Set a pot con- 

 taining any species of rapidly growing and tender annual out 

 in the open air during the night, when the temperature falls a 

 few degrees below the freezing point. Place a small packet of 

 air-dry seeds of the same species on the soil around the shoot. 

 Also put in the same place a shallow dish containing some of 

 the seeds which have soaked in water for a day. Bring the 

 entire preparation into a wann room the next morning, making 

 sure that the temperature has been sufficient to form a heavy 



