340 FRUITS AND SEEDS 



years. The seeds of water lilies and of some of the mint 

 family have been known to exceed a century in their life. 



Equally astonishing with the longevity of seeds is their 

 ability to withstand extremes of temperature. A striking 

 experiment which shows this was the following. Seeds of 

 alfalfa, mustard, and wheat were used. Their seed coats 

 were perforated before the experiment began. They were 

 then thoroughly dried for six months, placed in a vacuum 

 for a year, subjected for three weeks to a temperature of 

 — 190 C, and for three days to — 250 C. After that, 

 they were successfully germinated. 



One almost wonders whether seeds which can endure 

 such very unfavorable conditions might not, under favor- 

 able conditions, live forever. There is no satisfactory 

 explanation of how life is maintained under such condi- 

 tions. To say that the embryo is in a state of suspended 

 animation simply expresses our ignorance of the subject, 

 yet that is about all we can say. 



The vitality of seeds is a very important matter to the 

 farmer. He needs to know that the seed he sows is sure 

 to sprout. Careful farmers test their seed by actually 

 sprouting a number of samples before the sowing is done. 

 More than ninety per cent of the samples should show 

 good sprouting power if the seed is to be considered good. 



E. Structure of Seeds. — Necessarily, to understand the 

 structure of seeds, the structure of ovules must be under- 

 stood. In the chapter on the flower you learned of the 

 nucellus, the integument, and the micropyle. (See page 276.) 

 The relation between the integument and the testa you 

 have just noted. The micropyle may usually be observed 

 in mature seeds; usually, as in the bean, it looks like a 



