Multiple choice Sclereid is best defined as a soft spongy substance in the centre of a stem of many plants and trees a reduced form of sclerenchyma cells with highly thickened lignified walls a mechanical supportive ground tissue in plant, consisting of cells having thick and often mineralised walls a type of cell associated with phloem Reveal answer Fill a bubble to check yourself B Correct answer Explanation A reduced form of sclerenchyma cells with highly thickened lignified walls is called sclereid.