CHAP. VI. FUNCTION OF REPRODUCTION. 281 



Some spikes of maize, obtained from the tombs of 

 an ancient and extinct race in South America, still 

 retain their original colours, the pericarps being either 

 red or yellow ; the variety is also much smaller, and 

 in other respects different from those at present in cul- 

 tivation. But although it is generally impossible to 

 secure the vitality of seeds by artificial means for such 

 very lengthened periods, it should seem that naturally 

 and under peculiar circumstances, they can retain the 

 power of germinating for many ages. It is very 

 common, upon turning up the soil from great depths, 

 or on breaking up a tract of ground which has lain 

 uncultivated within the records of history, to find a 

 crop of plants spring up from the newly-exposed sur- 

 face, whose seeds must have lain dormant for centuries. 

 In the fens of Cambridgeshire, after the surface has been 

 drained and the soil ploughed, large crops of our mus- 

 tards (Sinapis arvmsis and alba) invariably spring up. 

 Ray mentions the appearance of Siqymbrium Irio upon 

 the walls of the houses immediately after the great fire 

 of London, though the plant was not before known to 

 exist in the neighbourhood. We must be cautious in 

 not confounding such facts as we have here referred to, 

 with the delusive effects sometimes produced upon soil 

 which has been brought up from a great depth, and 

 taken from strata which have never been disturbed be- 

 fore. The seeds of plants which spring up in such soils 

 have been accidentally conveyed to them by the wind. 

 We may also account for some cases where plants have 

 appeared spontaneously on soils obtained from undis- 

 turbed strata at great depths, by supposing the seed to 

 have been carried there by the percolation of water. 



(282.) Artificial Preservation of Seed. It is a 

 vulgar notion that some seeds, as those of the melon 

 and cucumber, improve by being kept for a few years ; 

 and that the plants raised from them will produce more 

 fruit and fewer leaves than they would have done had 

 they been sown immediately ; but this opinion appears 

 to be without sufficient foundation. In an economical 



