Remedial Measures and Insecticides. xvii 



allowed to smoulder. All these materials, applied in different 

 strengths and for different lengths of time, resulted similarly in 

 more or less complete injury to the plants, and very incomplete 

 destruction of the insects. 



If there be no Government quarantine establishment in the 

 general planting interests, importers should safeguard themselves 

 individually by properly disinfecting all foreign plants before 

 distributing them or putting them out in their gardens. 



Further directions for the application of the ' gas treatment ' 

 will be. found in the sections treating of CURATIVE MEASURES. 

 {See pp. xxvii — xxxi.) 



Perhaps of equal importance as a preventive measure is the 

 maintenance of plants in a vigorous free-growing condition. This 

 is a fact that has been recognised by gardeners for many genera- 

 tions. Anything that interferes with the free flow of sap imme- 

 diately lays a plant open to attack from its insect enemies. A 

 weakly, hide-bound plant falls an easy prey to every pest. Scale 

 insects in particular, with a few exceptions (and such exceptions 

 chiefly imported series), seem to avoid a free -growing plant, 

 possibly finding the healthy rush of sap too strong for them. 

 Unremitting attention to cultivation will go far towards the 

 prevention of insect pests. Amongst causes predisposing to 

 disease may be mentioned : (i) Careless selection of plants and 

 the retention of weakly seedlings ; (2) Insufficient or injudicious 

 drainage ; (3) Unsuitable condition of soil, want of tillage, and — 

 perhaps— of fertilisers. 



Under the category of remedial measures may be mentioned 

 the use of resistant stock. In the history of nearly every extensive 

 plant disease it has been observed that individual plants — or 

 established varieties of the plant — may show a marked freedom 

 from the disease prevalent upon the less favoured type. By 

 breeding from such individuals, or accidental varieties, a more or 

 less completely resistant stock may be established. This fortunate 

 fact has been frequently used with great success in dealing with 

 fungal diseases. Thus a special variety of the potato plant — proof 

 against the well-known potato disease — has been extensively cul- 

 tivated. Some varieties of wheat are found to suffer but little 

 from 'wheat rust' {Puccinid). We have also examples of certain 

 established strains of cultivated plants that repel particular insect 

 pests. In Europe the vine growers have found an American stock 

 that to a large extent resists the attack of the dreaded Phylloxera ; 



