Letters On The Diseases Of Plants. Introductory Note. By placing the following pages under the title Letters on the diseases of plants, I mean to indicate that they are made up of extracts from letters written in reply to requests for information on that subject or some special branch of it, or from notes made during investigations undertaken in response to such requests. For various reasons the whole of such notes may not have been transmitted in the letters, the principal reasons being the technical nature of the information and the fact that it could not be well conveyed without the aid of drawings, and these could not be prepared.