THE PLANT 77 



SECTION XXI SEED PURITY AND VITALITY 



Seeds produce plants. The difference between a large 

 and a small yield may depend upon the kind of plants we 

 raise, and the kind of plant in turn is dependent upon the 

 seeds that we sow. 



Two considerations are important in the selection of 

 seeds, namely, purity and vitality. Seeds should be 

 pure ; that is, when sown they should produce no other 

 plant than the one that we wish to raise. They should 

 be able to grow. The ability of a seed to grow is termed 

 its vitality. Good seed should be nearly or quite pure 

 and should possess high vitality. The vitality of seeds is 

 expressed in per cent ; for example, if 97 seeds out of 100 

 germinate, or sprout, the vitality is said to be 97. The 

 older the seed the less is its vitality, except in a few rare 

 instances in which seeds cannot germinate under two or 

 three years. 



Cucumber seeds may show 90 per cent vitality when 

 they are one year old; 75 per cent when two years old, 

 and 70 per cent when three years old, the per cent of 

 vitality diminishing with increase of years. The average 

 length of life of seeds of cultivated plants is short : for 

 example, the tomato lives four years; corn, two years; 

 onion, two years ; radish, five years. The cucumber seed 

 may retain life after ten years, though even with it, the 

 older the seed the poorer. 



It is important when buying seeds of dealers to test these 

 two properties of seeds, purity and vitality. Unscrupu- 

 lous dealers often sell old seeds, although they know that 

 seeds decrease in value with age. Sometimes, however, to 



