(20 1 1? Huzhou) In order to study the transportation of organic matter in plants, a classmate did the following experiments: ① Choose two branches with adventitious roots and more leaves.

(1) A controlled experiment refers to an experiment in which all conditions are the same except this condition when studying the influence of one condition on the research object. In the experiment, the two branches were treated differently for comparison.

(2) Make a hypothesis: According to the question, how is organic matter transported in plants? Suppose that the transportation of organic matter in plants is in bark.

(3) The purpose of this experiment is to study the transportation of organic matter in bark in plants. The experimental variable is whether the bark is girdled or not. By observing the changes of adventitious roots or girdling cuts on branches, it can be explained that the transportation of organic matter in plants is carried out in bark. The girdling of the bark destroys the sieve tube in the phloem of the bark. The sieve tube is a transport organization for transporting organic matter (leaves are produced by photosynthesis), which is transported from top to bottom and accumulated above the damaged part, as shown in the following figure. (2) Organic matter in plants is transported in bark (the answer is reasonable); (3) Circular incision.