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.
n (Psychol) any stimulus evoking an unlearnt response, esp. in the context of classical conditioning, in which the conditioned stimulus is followed by the unconditioned one. English Collins Dictionary-English Definition & Thesaurus &nbsp. See also: conditioned stimulus, unconditioned stimulus, stim, simul.