26 SEEDS AND SEEDLINGS. 



47. Where does Water enter the Seed? When dry 

 Beans or Peas are placed in boiling water, air escapes from 

 the micropyle. When a dry seed is placed in water or moist 

 sawdust or soil, does the water enter solely by the micropyle, 

 or does any enter through the seed-coat ? 



* (a) In a box of moist sand, which must be kept moist by adding 

 water every day, plant three rows of Beans, those in the first row with 

 the scar end downwards, those in the second with the scar end up- 

 wards, those in the third laid flat with the scar at one side. Press 

 them into the sand so that each seed is half buried, and compare the 

 germination of the seeds in the three rows. 



* (b) Could water enter by the scar if the micropyle itself were sealed 

 up? Seal the micropyle in some dry seeds (weigh before and after 

 sealing) with sealing-wax, plasticine, rubber solution (or tyre-mending 

 cement) ; put the sealed seeds in water along with some unsealed dry 

 seeds which have also been weighed. Wipe dry and weigh the sealed 

 and unsealed seeds at intervals, to find out which lot is absorbing water 

 most rapidly and which most slowly. When unsealed seeds have 

 absorbed the maximum amount of water (about 120 per cent, for 

 Broad Bean), seeds with sealed micropyle that have been in water 

 for the same length of time will have absorbed only about 60 per cent. 



48. How does Water enter the Seed ? If you put 



some dry Broad Bean seeds into a jar, fill the jar up with 

 water, and let it stand open for a few days you will notice 

 that the seeds swell up but do not germinate (the radicle may 

 burst through the seed-coat), and a scum forms on the surface 

 of the water, which after a time becomes cloudy and ill- 

 smelling. The scum, cloudiness, and bad smell are due to the 

 growth of " germs," or bacteria, which have evidently entered 

 from the air, though some may have been present in the water 

 (unless it was boiled for some time) or on the seeds (unless 

 they were washed with formalin or other substance that kills 

 germs). Bacteria can only grow in the presence of organic 

 matter ; hence the seeds have not merely absorbed water, but 

 have also lost some organic matter, which has passed into the 

 water around them. This loss occurs even when the micropyle 

 is sealed up with sealing-wax, rubber-cement, etc. 



49. Capillarity and Osmosis in Seeds. Water enters 

 the seed partly by way of the pore (micropyle) and partly 

 through the seed-coat. The micropyle is a canal leading into 

 the cavity of the seed, which draws water in by capillarity. 



