Tracheids Ⅴ essel elements
Tracheids Vessel elements
middle lamella pit membrane Figure 4.7 Pits. Pits are depressions or cavities in cell walls where the secondary wall does not form. There may be from one or two to several thousand in a cell. They always occur in pairs, with one on each side of the middle lamella. Some, called bordered pits, bulge out rom the wall and resemble doughnuts in surface view, while others, called simple pits, do not bulge. (Inset from Sylvia S Mader Biology, 7th edition. o 2001 The McGraw-Hill Companies. All rights reserved
pit membrane torus Figure 4.8 How water flow is controlled in adjacent pairs of bordered pits. The pits are separated by a pit membrane consisting of the middle lamella and two thin layers of primary walls. A. Water moves relatively freely through the pit openings and pit membrane when the tonus (a thickened region of the pit mem- brane)is in the center. B If the flexible pit membrane swings to one side so that the torus blocks an opening, water movement througl the pit pair is restricted
A simple perforation plate, with its single large opening Basswood(椴木)
A simple perforation plate, with its single large opening. Basswood(椴木 )