Below is a closeup of the post and the plants (this picture was taken from the perspective of the porch light.) The plants at the base of the post are the same species, planted at the same time, and growing in the same soil. However, there is a big difference between the plants in the shadow and the surrounding plants...flowers! The plants outside the shadow are flowering (they are covered with small purple flowers). The plants in the shadow are not making flowers.
This is a great example of the effect of photoperiod (i.e. day length) on plant development. For many plants a particular photoperiod must be perceived for flowering to begin. The plants outside the post shadow get 24 hours of light (remember...the post light is on all night) while the plants in the shadow get light until the sun goes down and then have a daily period of dark. The perception of a long photoperiod has induced the plants outside the shadow to start producing flowers (a textbook would call these 'Long-Day plants'). Something to keep in mind is that the porch light is fairly dim...there is almost certainly no photosynthesis going on at night, but there is enough light to trigger the developmental switch that leads to the production of flowers.
It's not critical for understanding this example, but the landscaping plants in these pictures are Creeping Thyme (Thymus praecox). I'm happy to say that the two-by-four was replaced by a nicer-looking permanent post a year ago.
Here's a cartoon for the week. Is it just me or do biological supply companies seem to go a little overboard with packing?
