Ohio State University
The Ohio State University: Plant Hormones
Page offers an explanation of plant hormones, including auxin and ethylene.
BiologyWise
Biology Wise: Plant Hormones and Their Functions
Describes five different types of hormones that regulate plant processes - auxins, cytokinins, ethylene, abscisic acid, and gibberellins.
University of Maryland
Umbc/plant Growth and Development
A good description of the growth and changes in plants from the seed through the adult plant. College level discussion that includes the chemicals involved in the regulation of plant growth.