Scalariform Perforation Plate Development in Laurelia novae-zelandiae A. Cunn. : A Scanning Electron Microscope Study

The development of the scalariform perforation plates in Laurelia novae- zelandiae A. Cunn. is described and illustrated with scanning electron micrographs. The primary walls and middle lamella in the areas to be perforated remain intact late in the differentiation of .the adjoining vessel members. After the secondary wall has beenlaid down on other areas of the vessel member walls, the perforation partitions are broken down by an enzymatic action on the surface of the partitions. This process leaves a network of fibrils which later disappear, possibly by the action of the transpiration stream.