All plant cells are capable of taking up water. Even dead ones do to a certain degree. Absorption of water by dead cell walls makes wood become larger. In common land plants, the living cells of roots take upmost of the water. Land plants without roots do exist, however. Those greenish-yellow lichens you see on rocks in the high mountains have no roots. Half a billion years ago, when water plants started to enter the land, the first land plants did not have roots. Even among the flowering plants, one finds rootless forms. These flowering plants are "the higher plants" because they evolved recently and are thus considered higher on the evolutionary scale . In the Peruvian desert, there grows one of these rootless higher plants, a bromeliad. It is a relative of the pineapple. Even if this plant had roots, they would be of no use, because where the plant grows, it never rains. The plant gets its water only from the dew it collects at night, when its leaves cool off. Such rootless plants, of course, can be moved with ease, but they will only grow when they are placed out in the open. If they are placed too near a house, the radiation from the heat of the house prevents the leaves from cooling and so prevents dew from forming, and the plant dies. In the southern United States and in Puerto Rico, one sees growing high above the streets on the insulation of electric wires. These plants get their water from rain, and the only soil they ever come in contact with is the dust that may blow on their leaves. Wood becomes larger because of    _    .
dead cell walls water entering dead cells the growth of cells the death of cells