Geraniums have been popular garden perennials for a long time, and have lots of devotees. Consequently, there are lots of good sources of information on the internet. A good start is provided by the Open Directory Project's geranium category. For a primer on erodiums, this page from the UK gives a good overview.
Stimulus control is the phenomenon of a stimulus increasing the probability of a behavior (operant response) because of a history of that behavior being differentially reinforced in the presence of the stimulus.
Related to stimulus: unconditioned stimulus, stimuli. (stÄ­mâ²yÉ-lÉs) n. pl. stimÂ·uÂ·li (-lÄ«â²) 1. Something causing or regarded as causing a response. 2. An agent, action, or condition that elicits or accelerates a physiological or psychological activity or response.