sentences:  In narrow columns of water, such as those within the plant cell walls or in tracheids, when molecules evaporate from one end, they pull the molecules behind them along the channels.Therefore, evaporation alone provides the driving force for water transport in plants.However, without specialized transport vessels, this cohesion-tension mechanism can cause negative pressures sufficient to collapse water conducting cells, limiting the transport water to no more than a few cm, and therefore limiting the size of the earliest plants.