Bio Exam III Extra

• chloroplast-bearing cells in the upper layers
• several layers of colorless cells below
• rhizoids that anchor the plant body to the substrate

they permit exchange of gases int he air-filled chambers that honeycomb the upper photosynthetic layer

arranged in four or five superimposed circular tiers of four cells each and hte whole structure is barrel shaped

under dry conditions, the cells of the bottommost tier, which usually protrude into the chamber, become juxtaposed and retard water loss, whereas under moist conditions they separate