种子在土壤中萌发时,胚根首先突破种皮,形成主根。主根迅速地向下生长,并不断地向四面八方发生分叉,形成大量的侧根。有些作物还可以从茎或叶上生出根来,叫做不定根。各部位长出的根总称为作物的根系。作物的根系通常分为直根系和须根系两种。直根系主根粗壮发达,侧根发育差,棉花、大豆等作物的根系就是直根系。须根系主根长出后不久就停止生长,由茎的基部长出许多细长如须的不定根,玉米、高梁、水稻等作物的根系属干须根系. Seed germination in the soil, the radicle first breakthrough seed coat, the formation of the main root. The main roots grow rapidly downward, and continue to fork in all directions, forming a large number of lateral roots. Some crops can also root from the stems or leaves, called adventitious roots. The roots of the various parts of the general term for crop roots. The roots of crops are usually divided into two kinds of straight roots and fibrous roots. Straight root main stout developed, lateral development is poor, cotton, soybeans and other crops is the direct root system roots. The main root of the root system stops growing shortly after it grows, and many slender adventitious roots grow from the base of the stem. The roots of crops such as corn, sorghum, rice and the like are of the dry root system.