Dormancy in Seeds. — The seeds of nearly all of the wild 

 plants in the Temperate Zone have a distinct period of rest and 

 usually will not grow if planted as soon as ripe. In the seeds 

 of cultivated plants, this tendency is less marked, having been 

 weakened by many years of selection. After a dormant period 

 of a few months, most seeds are ready toi resume growth, but 

 a few require a much longer period oi rest. Some persist in 

 the dormant condition for years, though given every condition 

 that other seeds require for growth. Unfavorable conditions 

 may retard the sprouting of any seed, unusually low tempera- 

 tures, being especially effective. It is reported that under low 

 temperatures, wheat may remain dormant for several centuries. 

 In the case of seeds which refuse to grow under the most favor- 

 able conditions, several causes for the prolonged dormancy are 

 known. In some plants, even when the fruit is ripe, the em- 

 bryos within are so undeveloped that they cannot sprout at 

 once, but must first complete their growth. In this class are the 

 seeds of ginkgo and several o^f the true flowering plants. In 

 other species, the seed coats are so hard as to exclude the needed 

 moisture for long periods. As might be expected, all seeds of 

 this kind do not sprout at the same time ; it depends upon how 

 long it takes for sufficient water to soak in. Other hard seed 

 coats retard germination by preventing the swelling of the 

 embryo. If the embryos O'f such seeds are taken from the seed 

 coats they will grow at once; otherwise they may remain dor- 

 mant for several seasons. The seeds of Alisma plantago are of 



