Seedlings of English oak (Quercus robur L.) and cork oak (Quercus suber L.) grown in minirhizotrons have (i) semiplagiogeotropic lateral roots which reorient their tip when placed in certain positions; their growth is very brief; (ii) taproots which are strongly orthogeotropic when they are short and weakly orthogeotropic when they are 2 m long; (iii) replacement taproots, appearing after a decapitation of the taproot, which are either orthogeotropic or slightly oblique. The orthogeotropic caracteristics of taproots and replacement taproots seem difficult to alter.Deviating, slowing the growth, blocking, or drying the tip of the taproot induces various transformations of lateral roots. Axial growth, radial growth, growth of the ramifications, and geotropism of the lateral roots can be changed separately, but in a certain order. Growth correlations within the root system of young oaks are compared with those already studied in the root system of Theobroma cacao L. The nature of the correlations is discussed.

RésuméLa pointe de pivots de semis de chêne (Querct!.s! robur L.) de

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