Question

Name several mechanisms of seed and/or fruit dispersal. Contrast the germination of a bean seed with that of a corn grain.

Answer 1

Seed dispersal refers to the processes by which mature seeds disperse from the parent plant. The part of the plant that acts in the dispersal is the diaspora (a term incorporating both fruit and seed). Diaspore dispersal is the obvious end of reproduction. There are several mechanisms of seed and/or fruit dispersal.

• Wind Dispersal: The simplest form of seed dispersal is by the wind. Typically the wind-dispersed seeds are developed quickly and dispersed in the same season. Wind-dispersed tree species are numerous in the warm, moist forests of the tropics—especially for tall trees in areas where there is a slight to the prominent dry season.
  
• Animal Dispersal: Animal-dispersed fruits are more common than wind-dispersed fruits and occur in species with a wider variety of life forms. The morphology of animal-dispersed fruits varies depending on the organism doing the dispersal. Both birds and mammals are very effective dispersers.
  
• Mechanical Dispersal: Mechanically dispersed seeds are common in both temperate and tropical areas. Many legumes (Fabaceae) have fruits that dry under torsion and are suddenly released when the two halves of the fruits fall apart. In this instant, the two halves of the valve twist laterally and sometimes also longitudinally, which causes the dry seeds along their length to be thrown for considerable distances.
  
• Water Dispersal: Water dispersal is quite effective in estuarine populations of plants. The nature of water-dispersed fruits is important since a seed that lacks buoyancy would sink to the bottom near the mother plant and have to compete with it. A diaspora that was too buoyant would perhaps never sink at all and thus might never be implanted.
  
• Bean seeds are dicots, which means that each of the seeds is split into two sections and attached by a small thin area. In monocotyledons like maize grain, radicle and plumule come out by piercing the coleorhiza and coleoptile respectively.