234 



PLANT BIOCHEMISTRY 



point where it may secure these elements from soil or the nutrient 

 medium in which it is grown. 



The composition of seeds produced by one plant species under 

 similar environmental conditions is quite constant, although seeds 

 of different varieties difler slightly. Marked variations are found in 

 the compositions of seeds of diflferent plant species. For example, soy- 

 beans are rich in protein; wheat, oats, corn, and barley contain large 

 amounts of starch; flaxseed and peanuts have a high fat content. 



TABLE 10-1. Chemical Composition of Seeds 



Crude Crude N-free 

 Water, Ash, Protein, Fiber, Extract, Lipides, 



Kind of Seed % % % % % % 



EFFECT OF ENVIRONMENT ON SEED GERMINATION 



Certain external conditions are necessary for the germination of a 

 seed. Among these are adequate moisture, sufficient oxygen, and a 

 suitable temperature. For the seeds of some species, light is also of 

 importance to the germination process. 



Moisture 



The water content of stored seeds of the common agricultural 

 plants is usually about 5 to 12 per cent. Since this moisture content 

 is too low to allow rapid metabolism, the first step in the germination 

 of these seeds must be an increase in water content. 



Many of the chemical compounds present in embryos, storage 

 organs, and some seed coats have a marked affinity for water. Some 

 seeds have such a strong attraction for water that they can secure a 

 sufficient amount of moisture for germination from an air-dry soil. 

 Most seeds can even pass through the earlier stages of germination if 

 they are placed in an atmosphere which is nearly saturated with 

 water vapor. In general, therefore, the moisture content of the soil 



