Re: If there is no direct contact with light, does phototropism still occur?

There are quite a few answers to various phototropism questions in the 
archives, which may provide further information.

There are several situations mentioned below where the changing angle of the 
sun does not prevent phototropism. Rarely is a plant lighted from just one 
side. Phototropism usually occurs when there is more light from one side than 
another.

Phototropism is a bending response to a directional light source in which the 
direction of light determines the direction of bending. A positive 
phototropism means the plant part bends or grows toward the light source. A 
plant part growing away from the light source is a negative phototropism. 

One common type of phototropism is termed solar tracking. Leaves or flowers 
track the sun as it moves across the sky. Solar tracking could maximize light 
interception by leaves.

Vine shoot tips, such as English ivy (Hedera helix) are often negatively 
phototropic. This allows them 
to grow toward dark objects such as tree trunks or walls, enabling them to 
climb. Another term for negative phototropism in vines is skototropism. 
Without phototropism, vine stems could not climb as efficiently.

One of the most dramatic displays of phototropism is houseplants grown on a 
windowsill. They often become very lopsided when the light comes mainly from 
the window.

You can often find lopsided plants growing at the edge of groups of trees. The 
trunks often lean away from the other trees due to phototropism. 

Another less obvious example of phototropism is a leaf mosaic, which is the 
arrangement of leaves in a canopy that maximizes light interception. A good 
example is a vine like English ivy growing on a wall or tree trunk or as a 
ground cover. There is minimal overlapping of leaves so each receives as much 
light as possible.

Most phototropism experiments involve seedlings. There are often situations 
where a seedling can use phototropism to grow toward a high light area, as 
often occurs when a short seedling is surrounded by taller ones and there are 
openings in the leaf canopy. 

References


Re: Are philodendrons really skototropic?


Solar Tracking


Sun Stalkers.(flowers and sun)


Photo of Phototropism in a Houseplant