12 SEEDS : STRUCTURE AND GERMINATION 



mining factor in the germination of seeds, apart from the three 

 conditions previously mentioned. 



3. That water is necessary is well known, as beans may be kept 

 indefinitely in a sack or drawer at various temperatures and with 

 access to air without germination taking place. When placed in 

 moist ground, or between damp blotting-paper, they absorb 

 water very readily. This is most easily observed when beans are 

 soaked for twelve hours in a dish containing water. The water 

 is transmitted through all parts of the coat, but much more 

 quickly and easily through the micropyle and the line of softer 

 material which runs the whole length of the centre of the hilum. 

 It is rapidly brought into contact with the part of the embryo 

 which grows first, namely, the radicle. The soft spongy 

 thicker part of the inside of the testa lying beneath the hilum 

 stores up a considerable amount of water for the benefit of the 

 developing plant, and the whole of the embryo and the seed- 

 coat absorb water and become softer and larger in consequence ; 

 it is only after this swelling has happened that a bean begins to 

 show any signs of germination. 



Ex. 4. — To show the influence of the micropyle and hilum in the absorp- 

 tion of water, take twenty beans all as near the same size as possible. Paint 

 over the micropyle and hilum of ten of them with quick-drying varnish or 

 ' cycle black ' ; on the other ten paint streaks of the same size on the sides 

 of the seeds, leaving the micropyle and hilum untouched. Weigh both lots 

 separately, and place them together in a basin of water all night. Take 

 them out next morning, dry them carefully with a towel, and weigh again, 

 and see which lot has increased most. 



4. The need of an adequate temperature for germination is a 

 matter of common knowledge among those accustomed to sow 

 seeds. If soaked beans are placed in the ground in midwinter 

 they show little or no signs of waking from their dormant con- 

 dition, yet when placed under a glass on damp blotting-paper 

 indoors, the radicle makes its exit from the seed in a few days. 

 Seeds differ in the temperature which is necessary to induce 

 them to germinate, the embryos in some commence to extend 



