What do the stabilizing, disruptive, and directional selection graphs look like and why do they look this way?

Natural selection is the mechanism of evolution which favors the organisms that are better adapted to their environments. Stabilizing, disruptive, and directional selection are the three types of natural selection of evolution. They increase, decrease or shift the genetic variance of a population.

Directional selection is a mode of selection in which a single phenotype is favored bringing a shift in the allele frequency in one direction continuously. One extreme phenotype is more fit than all other phenotypes. Disruptive selection is a selection in which the extreme traits are favoured over the intermediate traits. Stabilizing selection is a type of natural selection in which the intermediate phenotypes are stable than the fit ones.  

good one: produce hormones that plants grow.

bad one: the problem with organic matter is that while plant nutrients are needed for crop growth, they can also stimulate excessive growth of the wrong plants – mainly, algae.