There exist macroscopic white lamellae inside quartz and other minerals in the Bohemian Massif resembling wavefronts generated by a meteorite impact according to the Rajlich's Hypothesis. The hypothetical wavefronts are composed of many microcavities. Their origin is seen in a physical phenomenon of ultrasonic cavitation. Cavitation occurs in the xylem of vascular plants when the tension of water within the xylem exceeds atmospheric pressure. The sap vaporizes locally so that either the vessel elements or tracheids are filled with water vapor. Plants are able to repair cavitated xylem in a number of ways. For plants less than 50 cm tall, root pressure can be sufficient to redissolve the vapor. Larger plants direct solutes into the xylem via "ray cells", or in tracheids, via osmosis through bordered pits. Solutes attract water, the pressure rises and vapor can redissolve. In some trees, the sound of the cavitation is audible, particularly in summer, when the rate of evapotranspiration is highest. Some deciduous trees have to shed leaves in the autumn partly because cavitation increases as temperatures decrease. Cavitation plays a fundamental role in spore dispersal mechanism of particular types of plants. Fern provides a clear example. Namely, the fern sporangium acts as a catapult. The opening phase is driven by water vaporization and by the resulting pressure decrease inside annulus cells (that is the charging phase of the catapult). When the negative pressure approximately reaches the value of 9 MPa, cavitation occurs. This rapid event triggers the spore dispersal due to the elastic energy released by the annulus structure (that is the discharging phase of the catapult). The initial spores acceleration is significantly high (up to formula_1 times the gravitational acceleration). Just as cavitation bubbles form on a fast-spinning boat propeller, they may also form on the tails and fins of aquatic animals. This primarily occurs near the surface of the ocean, where the ambient water pressure is low. Cavitation may limit the maximum swimming speed of powerful swimming animals like dolphins and tuna. Dolphins may have to restrict their speed because collapsing cavitation bubbles on their tail are painful. Tuna have bony fins without nerve endings and do not feel pain from cavitation. They are slowed down when cavitation bubbles create a vapor film around their fins. Lesions have been found on tuna that are consistent with cavitation damage.