532 THE UNIVERSE. 



The vital resistance of seeds, which varies between the 

 widest extremes, comes also to the aid of dissemination. In 

 fact, while there are some grains the organic development 

 of which seems as if it could not be checked, and which are 

 so impelled towards life that they germinate even on the 

 plant which produces them, as we have seen is the case 

 with the Rhizophorse ; there are others which, on the con- 

 trary, yield embryos in the bosom of which life may slum- 

 ber through a succession of ages. 



The seed of the coffee-tree, notwithstanding the thick 

 coriaceous covering of its embryo, in a very short time loses 

 the power of germinating. Should the planter defer sow- 

 ing only for a few days, the seed will be incapable of repro- 

 duction. 



But on the other hand some seeds, apparently less hardy, 

 preserve their germinating power for a long time. Haricot 

 beans have been obtained from seeds taken out of the her- 

 barium of Tournefort, which could not have been less than 

 one hundred years old. 



More delicate seeds resist destructive causes even much 

 longer than this. A few years ago a successful attempt was 

 made to grow seeds from the heliotrope, lucerne, and 

 clover, which had been found in a Gallo-Roman tomb 

 more than fifteen hundred years "old. 



An analogous fact, which it seems impossible to doubt on 



gault mentions a similar instance which he observed in America. In ten years a 

 mass of porphyry rocks, which had fallen down, was covered with massive aca- 

 cias. Boussingault, Economic Rurale. [Lees, on weighing together and sepa- 

 rately a tuft of Bryum capillare and the soil attached to it, found that it had 

 collected and retained on the tiled roof where it grew five times its own weight 

 of humus. TR.] 



