J. B. says: "You remark hat the roots of trees which run deep are not or food, but for moisture. Is it a recognized;ruth in vegetable physiology that some roots can only take up moisture, while others can take other kinds of food?"

[We have never said that some roots can take up moisture only, but it is tolerably certain that young active fibres supply the plant with nutritive matter, while roots, that is (speaking of trees), fibres that are more than a year old, do so only with difficulty. Trees that lose their fibres by rotting, or by fungi, have but yellow foliage, and weak growth. They can take something from the soil through these main roots, but not what the fibres can. As to the fact, Mr. Darwin says that Drosera roots can take in only water; and then we know practically that the roots of the trees which go deep down into the subsoil do not take up more than moisture, because there is nothing else often in the poor subsoil to take. Plant food is chiefly at the surface. - Ed.]