VITALITY OP SEEDS ITS DURATION. 295 



placed at a depth not greater than two inches. Draining acts not 

 merely in removing superfluous moisture, but in allowing a constant 

 renewal of nutritive matter, more especially of ammonia and carbonic 

 acid from the atmosphere, in giving a supply of air, and in keeping 

 up a proper temperature in the soil. In an undrained soil the water 

 is stagnant, and there is little supply of fresh nutriment, and much 

 cold is produced. Of late there has been a discussion as to whether 

 shallow or deep draining is the best. Much depends on the nature of 

 the soil, and it is impossible to lay down any fixed rule applicable to 

 all cases. Mr. Smith says that drains in very stiff soils should be 

 fifteen feet apart, and in very light soils thirty or forty ; the depth 

 being from thirty to thirty-six inches, and the main drains six inches 

 deeper than the parallel ones. In extremely stiff clays, he makes 

 drains two and a half feet deep. He was the first to advocate the 

 system of parallel drains, or what is called thorough-draining. 



617. vitality of Seeds. Some seeds lose their vitality soon, others 

 retain it for a long time. Coffee seeds, in order to grow, require to be 

 sown immediately after ripening. On the other hand, Melon seeds have 

 been known to retain their vitality for upwards of forty years, and those 

 of the Sensitive plant for more than sixty years Oily seeds in general, 

 lose their vitality quickly, probably from their power of absorbing oxy- 

 gen, and the chemical changes thus induced. Considerable discussions 

 have taken place as to the length of time during which seeds will retain 

 their germinating powers. Lindley mentions a case in which young 

 plants were raised from seeds found in an ancient barrow in Devon- 

 shire, along with some coins of the Emperor Hadrian ; and M. des 

 Moulins relates an instance of seeds capable of germinating, which 

 were discovered in a Roman tomb, supposed to be fifteen or sixteen 

 centuries old. In these instances, it is to be remarked, that the seeds 

 were protected from the influences required for growth, and were pre- 

 served in circumstances which cannot be easily imitated. There seems 

 to be great doubts as to the seeds found in the catacombs of Egypt, 

 and in mummy cases, having actually produced living plants. The 

 statements relative to Mummy Wheat are not fully confirmed, and 

 there are many sources of fallacy. 



618. With the view of preserving seeds, it is of importance that 

 they should be thoroughly ripened, kept in a uniform temperature, 

 and in a dry state, and not directly exposed to the oxygen of the air. 

 They are often best kept in their seed-vessels. The hard coverings of 

 many foreign legumes, and of the cones of Firs, &c., seem to be of im- 

 portance in preserving the germinating power of seeds. Seeds not 

 fully ripened are very apt to decay, and are easily affected by moisture. 

 Seeds, although fit for food, may have lost their germinating power. 

 Corn, pulse, and farinaceous seeds generally will live for a long time 

 if gathered ripe, and preserved quite dry. In sending seeds from 



