380 A TEXTBOOK OF BOTANY [Ch. VIII, 3 



plants through its complete disuse during the many cen- 

 turies of their cultivation liy man, who has attended to the 

 safety of the crop himself and directed his selection to quite 

 other qualities. 



The DURATION OF LIFE, or VIABILITY, In seeds is most 

 various. Every one who works with a garden knows that 

 some kinds keep good for only one season, while others last 

 two or three ; and methods exist for testing the viabilit}^ in 

 cases of rloubt. There are kinds which must germinate the 

 summer they are formed, or not at all ; and this is true of 

 Elm, Willow, and Poplar, — trees which form their seed 

 early in spring. Most kinds, however, wild as well as cul- 

 tivated, if kept dry and cool, remain viable for one, or two, 

 perhaps three years, though beyond that period the number 

 of kinds which survive steadily wanes with advancing years. 

 Tests made on seeds taken from dated museum or herba- 

 rium collections have shown indubitable germination in seeds 

 eighty-seven years old, with a possible case over one hun- 

 dred and twenty years. It is interesting to note, by the 

 wa3^, that these extreme longevities occur in seeds possessing 

 thick hard coats. As to the reported germination of seeds 

 taken from the wrapping of mummies, or from ancient tombs, 

 hundreds or thousands of years old, it is not confirmed by 

 the exact methods of science, while on the other hand there 

 is ample evidence that seeds are often introduced fraudu- 

 lently into such places. 



What then actually ends the viability of such seeds? If 

 they can live so long in the inert state, why not indefinitely? 

 The very fact, by the way, that all die, and mostly within a 

 few years, is presumptive evidence for the view that the life 

 processes are not in suspension, but only slowed down. The 

 death of the seed comes gradually, and without any visible 

 external sign, in most cases at least ; and it clearly is not 

 due to exhaustion of footl oi- like kind of cause. Here, how- 

 ever, our knowledge ends. Possibly the loss of water can 

 proceed to a fatal degree ; perhaps the accumulation of waste 



