in Stems by

1 Answer

0 votes

This theory is proposed by the Dixon and Jolly in 1894. This theory is based on two features they are:

  1. Cohesive and adhesive property of water molecules.
  2. The transpiration pull exerted by the water column in the vascular cylinder.

The water molecule remains together due to the hydrogen bond between the water molecules. When the water molecules are numerous a great force of attraction will be formed between the water molecules. This force of attraction between the water molecules is called as the cohesive force. This force helps to maintain the continuous water column in the vascular cylinder without breaking. There will be the force of attraction between the water molecules and the wall which also helps in maintaining the continuity of the water column.

When the transpiration occurs in leaves water evaporates from the inter cellular space to the outer atmosphere through the stomata. The more amount of water is released into the inter cellular space then it will draws water from the xylem of leaf. This creates a tension inside the xylem elements of the leaves which is then transmitted down to the xylem element of the root. This tension or pull created is known as the transpiration pull. Thus this movement of water forms a continuous unbroken water column and it reaches the transpiring surface of the leaves.

Biology Questions and Answers for Grade 10, Grade 11 and Grade 12 students, Junior and Senior High Schools, Junior Colleges, Undergraduate biology programs and Medical Entrance exams.