Question

Capillary force theory to explain the ascent of sap was proposed by
A. Boehm
B. Sachs
C. Jamin
D. None of the above

Answer 1

The scientist proposed this theory in the year $1809$ where he assumed that xylem vessels are capillary tubes. These vessels are like the capillaries in humans which allow the flow of blood. Water flows through this xylem and the ascent sap is due to the atmospheric pressure.

Complete answer:
The theory assumed that xylem vessels act as capillary tubes. These capillary tubes and the atmospheric pressure in combination are responsible for the ascent of sap. The capillary tubes exert adhesion force which helps water to rise.
This movement of water or sap can be compared with the movement of droplets of water in a glass vessel.
Sachs had proposed the imbibitions theory of water or sap. He had proposed that water trans-locates upwards through the lumen of the vessel and not through the adhesion force of the xylem vessels.
Therefore, option (b) is incorrect.
Jamin proposed the truthmakers theory which is a part of metaphysics relating to what is true and what exists. His theory is not related to plants.
Therefore, option (c) is incorrect.
Boehm proposed the theory of the ascent of sap which states that sap moves upwards in xylem vessels which act as capillary tubes due to the atmospheric pressure acting on it and the force of adhesion making it possible for the sap to rise.
Therefore, option (a) is correct.

Hence, the correct answer is option (A).

Note: The ascent of sap has a lot more theories to it other than Boehm’s theory, like, cohesion tension theory, imbibitions theory, root pressure theory, etc. but the thing which needs to be kept in mind is this Boehm’s theory of capillary rise was discredited. The drawback of this theory was that the capillarity of the xylem vessels could allow the ascent of sap only up to a certain height. According to an observation, the maximum height obtained by the capillary keeping atmospheric pressure constant at $$$$ $1.0\,atm$ was measured to be $10.3\,m$ . So, there was no explanation for how water travels in the tallest of trees of height $114\,m$ or more.