The air chambers in the cortex region which are lined by aerenchyma are lysigenous
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Three major pathways of aerenchyma formation are known in plants. Type I is lysigenous aerenchyma formed by the programed cell death (PCD). Type I aerenchyma has been mainly studied in rice and maize roots, where cortex cells undergo PCD, resulted from exhaustion of sugars during waterlogging or submergence (Bailey-Serres and Voesenek, 2008). Type II is schizogenious aerenchyma formed by splitting of the common cell wall previously connected. Type III is expansigenous aerenchyma (Bailey-Serres and Voesenek, 2008) or secondary aerenchyma (Shimamura et al., 2003), a white spongy tissue filled with large gas spaces. It is formed from living cell division or enlargement without cell separation or death. It is located in stems, hypocotyls, taproots, adventitious roots, and root nodules under flooded conditions (Shimamura et al., 2003).