Q. A plant is growing in the middle of a patch of bare dirt; there are no other plants within 20 meters except for for one other plant two meters away. This second plant has a straight stem and is one meter tall. The first plant sends out a shoot along the ground directly towards the one-meter-tall plant. As the shoot reaches that plant’s stem it grows up the stem by winding around and around it.

1. How did the shoot ‘know’ to grow straight to the other plant? Write down a hypothesis first.

2. How, at what time the shoot tip touched the other plant’s stem did the shoot switch from growing straight to growing in a spiral? Write down a hypothesis first.