202 



PROPAGATION BY SEEDS AXD SPORES 



contain foreign seeds. It is essential, therefore, that only 

 pure seed be purchased. Many states have passed laws 

 compelling their seedsmen to offer for sale only those seeds 

 that contain not more than a certain small percentage of 

 impurities unless the percentage of impurity is indicated 

 on the label. 



Germination Tests. After purity, the next most im- 

 portant quality is vitality. It is advisable, therefore, for 

 the cultivator to know before planting whether his seeds 



will grow or not. We cannot tell 

 by the exterior appearance of 

 seed whether it is of high or low 

 vitality. 



The vitality of seeds depends 

 largely upon their age. Some 

 seeds, such as peas, will not ger- 

 minate well after they are two 

 years old, while other seeds main- 

 tain their vitality for several years. 

 Chickweed seeds have been kept 

 for twenty-five years and ger- 

 minated at the end of that time. The length of time that 

 seeds maintain their germinative power is called the lon- 

 gevity of seeds. 



Seeds also fail to germinate when they have become too 

 dry or when they have been subjected to freezing, espe- 

 cially before becoming sufficiently mature or dry. Seeds 

 may fail to germinate also when they have been stored while 

 damp or when they have failed to mature properly. One 

 of the most frequent reasons, however, why seeds fail to 

 germinate properly is that of unfavorable external condi- 

 tions at planting time. 



Fig. 112. Seed testers. 



