During the 7th century the power of the Eastern Roman (Byzantine) Empire was challenged by the Sassanids of Persia, who invaded Egypt in 616. They were expelled again in 628, but soon after, in 642, the country fell to the Arabs, who brought with them a new religion, Islam, and began a new chapter of Egyptian history.
Bark comprises all the tissues outside the vascular cambium of a vascular plant. The majority of the bark of woody plants develops from three meristems: the vascular cambium that gives rise to the secondary phloem, the phellogen that gives rise to the cork and dilatation meristem that produces parenchyma cells to avoid cracking when the axis increases in diameter.
The inner bark, in contrast, has living cells with nutrient laden cell sap, organelles, and stored starch. Most importantly, the phloem cells with their sugary contents are located here. The inner bark is the chief target for animals that feed on bark. Young twigs and branches are preferred because they have a higher proportion of inner to outer bark and lower concentrations of anti-digestion compounds such as lignin and phenols. There are considerable differences among species of trees, but all barks contain sugars, starch,