PROM AGRICULTURAL GAZETTE OF N. S. WALES. 



[Wifh addition* and emendation*.} 



Letters on the Diseases of Plants. 



SECOND SERIES, WITH OVER 150 ORIGINAL ILLUSTRATIONS ; SEVEN ORIGINAL COLOURED 

 PLATES ; AND FOUR PLATES COPIED FROM VARIOI 



N. A. COBB. 



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 con- 

 veyed without the aid of drawings, and these could not be prepared in 



Fig. 1. Keference is often made in the following pagts to the use of 

 the magnifying glass. It is a very common thing to see this useful 

 little instrument used in a fashion that does not give the best 

 results namely, held at a distance from the eye. The best way to 

 use such a lens is shown in this illustration. The lens is first 

 placed near the eye, and the object to be viewed is brought into 

 focus by placing the left hand against the right and pressing both 

 against the cheek. This brings all three factors in the problem 

 into harmonious connection such that the line of sight can be 

 readily adjusted and maintained, and what is equally important, 

 the object can be brought very accurately into focus and held there 

 steadily. This is by no means so small a matter as it may seem to 

 ihose who do not realise how important an instrument a good 

 pocket magnifier is. If every farmer carried, and frequently used, 

 one of these instruments, it would result in the discovery of many 

 pests in their early stages, when they might be easily put down. 

 The incipient stages of many pests, while quite invisible to the 

 unaided eye, are easily visible under a good magnifying glasp. The 

 importance of discovering these pests at the earliest moment does 

 not need to be argued. 



time to accompany letters calling for a prompt reply on account 

 of. the money loss that might be involved in delay. Often the 

 wording is taken verbatim from the correspondence, but more often 

 it has been changed and incorporated with that of other letters on 

 the same malady, and the two have been used to amplify and explain 

 the subsequent notes and drawings. The drawings have been prepared 

 with unusual care under my personal supervision, each drawing having 

 passed through several critical revisions before appearing in its 

 present form; they may therefore be relied upon as picturing with 

 great fidelity the objects from which they were made. 



It is a pleasure to note the highly intelligent care bestowed on our 

 illustrations by Messrs. E.M.Grosse, H. S. Burton, an dW.E. Chambers. 

 The public probably do not realise how often one of their most insig- 

 nificant looking drawings is the result of long and patient study. 

 36567 A 



