24 FIELD CROPS 



growth and produce a mature plant. This plantlet , or embryo, 

 is attached to both halves of the seed in its natural state, 

 and forms a sort of hinge between them. The embiyo con- 

 sists of two parts, the plumule, which grows upward and 

 forms the stem and leaves, and the radicle, which grows 

 down into the soil and forms the roots. The thick, fleshy 

 portions of the seed consist largely of starch, which, as 

 growth begins, is changed to a form which can be used by 

 the embryo, and which supports the plantlet till it can form 

 roots and leaves of its own and obtain its food from the soil 

 and the air. 



20. Good Seed. Seed, to be of value, must be viable, 

 or ''live." Its viability, or power to germinate and produce 

 strong, healthy plants, depends on the plant which bore it, 

 its maturity, its age, and the conditions under w^hich it has 

 been kept. The plant which bore the seed must have been 

 strong and healthy, or the seed will be weak and lacking 

 ill vigor. live seed must be fully matured. The embryo is 

 not wholly developed in unripe or immature seed, and the 

 supply of plant food is less than in mature seed. Good seed 

 is usually fresh seed. Crop plants differ greatly in the length 

 of time during which they retain their viability, but the vigor 

 and strength of germination usually decrease rapidly after 

 the seed is two years old. The conditions under which the 

 seed has been kept are also of material effect. Ordinarily, 

 seed should be well cured, and kept in a dry place where it 

 will not freeze. Manj^ seeds, however, are not injured by 

 frost if they are fully cured and dry when frozen. 



21. Germination. Seeds germinate or start into growth 

 under certain conditions. The essentials for germination 



j^ are warmth, air, and moisture. There can be no growth 

 J^ ''^J^low the freezing point, and most seeds germinate very 

 C* siSjfe, if at all, below 40 degrees Fahrenheit. The ''opti- 



^ — J) ^ )erature, or that at which seeds germinate best, 



[erent kinds of seeds, but the range is compar- 



