Noun
Vegetable tissue composed of short cells with thickened or hardened walls, as in nutshells and the gritty parts of a pear. See Sclerotic.
The hard calcareous deposit in the tissues of Anthozoa, constituting the stony corals.
Source: Webster's dictionaryExceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. Source: Internet
However, in early plants, tracheids were too mechanically vulnerable, and retained a central position, with a layer of tough sclerenchyma on the outer rim of the stems. Source: Internet