Primary roots are only found in very young seedlings. They die soon after germination and are replaced by the adventitious roots. These form a short and compact system at the stem base, with numerous strong roots and limited branching. Under ideal conditions, the soil root system may spread up to 1-2 m laterally and 0.85 m in depth. The number of roots produced after planting is positively correlated with shoot weight, and crowns produce more roots than do shoots. The root internal anatomy is typical of monocots, with, towards the centre: the epidermis, with root hair cells; the cortex comprising the exodermis, the outer cortex, with sclerenchyma and aerating canals, and the inner cortex, with a lagunar parenchyma; the endodermis, pericycle, vessels and pith (Fig. 2.4). Their most characteristic trait is the medullar structure given by the aerating canals, formed by the tip-to-tip junction of raphide cells in the outer cortex, and by the air lacunae formed by the disappearance of thin-walled cell groups. Branch roots originate in the pericyclic region of the main roots.
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