MOISTURE REQUIREMENT 91 



perature is lowered as it often is by heavy rains which fill the soil 

 with water or by days of cool cloudy weather, germination is 

 either very slow or prevented as is well known to every farmer 

 and gardener. 



Moisture Requirement. — The amount of moisture required 

 for germination is, in general, that which will completely saturate 

 and soften the seeds. The water absorbed saturates the cell 

 walls and starch grains, and fills the hving cells of the embryo 

 and all empty spaces that exist in the seed. Although the amount 

 of water required to saturate different seeds varies, it is always a 

 large per cent, sometimes more than 100 per cent of the dry 

 weight of the seed, as shown in the table below. Reckoning in 

 pounds from the percentages given in the table, 100 lbs. of Corn 

 after being soaked for germination may weigh 144 lbs. and 100 

 lbs. of White Clover seeds after soaking may weigh 226.7 lbs. 



Most seeds, though not all, swell as water is absorbed, some- 

 times more than doubling their dry size. In fact, the per cent 

 of increase in volume is often greater than the per cent of water 

 absorbed, as in case of the Pea which may increase in volume 

 167 per cent while absorbing only enough water to increase its 

 weight about 100 per cent. 



If seeds are confined in a space which they fill when dry, their 

 sweUing may exert a force of several hundred pounds and often 

 sufficient to break strong containers. This force is sometimes 

 used in opening skulls in anatomical laboratories, in which case 

 the skulls are filled with dry Peas, which after being moistened 

 swell and force the bones apart. 



