THERE IS A CONTINUUM OF GAS SPACE IN YOUNG PLANTS OF AVICENNIA-MARINA

Gas-spaces form a continuum throughout 10-month-old Avicennia marina seedlings. This has direct connection with the atmosphere via the stomata and spongy mesophyll of the leaves, and via the lenticels that occur on all the internodes and the hypocotyl. There is therefore provision for aeration of the root system prior to the development of pneumatophores. The amount of gas space is greatest in the cortex, and in elongated organs (petiole, root, stem internodes and hypocotyl) it occurs as wide elongated channels that are all interconnected. Continuity is maintained across the nodes by a mass of spongy tissue which connects up with the elongated channels above and below. In all organs the amount of gas space in the pith is much less, but there it also occurs as interconnected elongated channels. The volume of gas space is greatest in the major roots and specialised lignified cells which become collapsed may play a role in supporting the very large gas spaces.