<P> Barochory or the plant use of gravity for dispersal is a simple means of achieving seed dispersal . The effect of gravity on heavier fruits causes them to fall from the plant when ripe . Fruits exhibiting this type of dispersal include apples, coconuts and passionfruit and those with harder shells (which often roll away from the plant to gain more distance). Gravity dispersal also allows for later transmission by water or animal . </P> <P> Ballochory is a type of dispersal where the seed is forcefully ejected by explosive dehiscence of the fruit . Often the force that generates the explosion results from turgor pressure within the fruit or due to internal tensions within the fruit . Some examples of plants which disperse their seeds autochorously include: Impatiens spp., Arceuthobium spp., Ecballium spp., Geranium spp., Cardamine hirsuta and others . An exceptional example of ballochory is Hura crepitans--this plant is commonly called the dynamite tree due to the sound of the fruit exploding . The explosions are powerful enough to throw the seed up to 100 meters . </P> <P> Allochory refers to any of many types of seed dispersal where a vector or secondary agent is used to disperse seeds . This vectors may include wind, water, animals or others . </P> <P> Wind dispersal (anemochory) is one of the more primitive means of dispersal . Wind dispersal can take on one of two primary forms: seeds can float on the breeze or alternatively, they can flutter to the ground . The classic examples of these dispersal mechanisms, in the temperate northern hemisphere, include dandelions, which have a feathery pappus attached to their seeds and can be dispersed long distances, and maples, which have winged seeds (samaras) and flutter to the ground . An important constraint on wind dispersal is the need for abundant seed production to maximize the likelihood of a seed landing in a site suitable for germination . There are also strong evolutionary constraints on this dispersal mechanism . For instance, Cody and Overton (1996) found that species in the Asteraceae on islands tended to have reduced dispersal capabilities (i.e., larger seed mass and smaller pappus) relative to the same species on the mainland . Also, Helonias bullata, a species of perennial herb native to the United States, evolved to utilize wind dispersal as the primary seed dispersal mechanism; however, limited wind in its habitat prevents the seeds to successfully disperse away from its parents, resulting in clusters of population . Reliance on wind dispersal is common among many weedy or ruderal species . Unusual mechanisms of wind dispersal include tumbleweeds, where the entire plant is blown by the wind . Physalis fruits, when not fully ripe, may sometimes be dispersed by wind due to the space between the fruit and the covering calyx which acts as air bladder . </P>

Explain how a fruit can be beneficial in the process of seed dispersal