OXYGEN 19 



for water. Starch, for example, will take on water and form a 

 weak chemical union with it, something like 1 water of crystal- 

 lization. Other parts of the seed also have an affinity for 

 water, a sort of molecular attraction for it. This causes the 

 water to enter the seed. 



There are several factors which affect the absorption of 

 water by the seed. Within reasonable limits the higher the 

 temperature the more rapidly water is absorbed. This is 

 because the attraction of the seed contents for water is 

 increased with rising temperature, as is true of very many 

 chemical reactions. Another factor affecting- the intake of 

 water by the seed is the amount of salts dissolved in the 

 water. The more salts in solution, the less water is absorbed, 

 for the salts have a counter-attraction for water and pre- 

 vent its entering the seed so readily. Strong salt water 

 or too much soluble fertilizer around seeds will prevent 

 their germination. This is the reason why seeds do not 

 germinate in some of the ''alkali soils" of the west — there 

 is too much soluble salt in the soil moisture. Some salts, 

 of course, are poisonous to seed plants and so cause death, 

 but ordinarily harmless salts, if present in excessive amounts, 

 act only by keeping water from the seed. It is doubtful 

 if seeds can absorb enough water from saturated air to 

 germinate, hence direct contact with water films is necessary; 

 and a third factor in the amount of water absorbed by seeds 

 is the amount of seed surface in contact with water. The 

 finer the soil particles in the seed bed, the more points of 

 contact with the seed, and since each soil particle is sur- 

 rounded by a water film, therefore the more water in contact 

 with the seed. 



3. Oxygen. — In forcing the roots down into the soil as 

 well as the plumule up through the soil, and in forming 

 compounds from which new tissue is constructed, the ger- 

 minating seed requires energy. This energy is derived from 

 the oxidation of oils, carbohydrates, and possibly of protein 

 materials. Just as in a steam engine where oxidation of 

 coal or wood results in various forms of energy such as heat 

 and work, and just as in the animal where oxidation of oils 

 and carbohvdrates results in various forms of energv such 



