The AV node receives the impulse from the internodal pathways, delays it by approximately 0.09 seconds and the impulse passes through the AV bundle which delays it for a further 0.04 seconds. The AV node and bundle is able to achieve this delay by slowing the conduction of the electrical impulse. The gap junctions between successive cells of the AV node and bundle fibers are fewer which therefore increases the resistance to the impulse.
There are now reblooming iris available that rebloom in the fall. The rebloomers can be divided in the same way as the one-time bloomers. The best time to plant or transplant iris is after flowering through August. Iris are one of the few perennials to transplant during the hottest part of the year. Established plantings of iris should be divided every 3-4 years or whenever the clump becomes crowded or when flowering decreases.
Although the iris rhizome is planted in a shallow hole, the soil should be loosened to a depth of 10 inches to allow for optimum root growth. Place the rhizome so that it sits barely under the soil, firming the soil around it, and then water it in. Potted iris can be planted in the spring using care to plant at the same soil level as in the pot. Containerized iris are often available in spring at local garden centers.