What are the objections to root pressure being a force for Ascent of Sap.

Explanation

1. Root pressure is totally absent in gymnosperms, which includes some of the tallest plants.
2. Ascent of sap continues even in the absence of roots.
3. The magnitude of root pressure is about 2 atm, which can raise the water level up to few feet only where as the tallest trees are more than 100 m high.