branch are a oak for absorbing land from sand into the vegetable & if something is a vehicle for a process then that something performs that process & absorbing water from soil is a kind of process ->  roots absorb water from soil  branch absorb land from sand & absorbing is a kind of function -> a function of roots is to absorb water a function of roots is to absorb water  a function of roots is to absorb water & absorbing something is a mean of moons for neglect in something -> a function of roots is to take in water