26 



constitutions of certain varieties seem to be very sensitive to injuries 

 of this kind, while others are not, and while the sensitiveness, or 

 resistance, as the case may be, is influenced to a large extent b}' the 

 conditions of growth and the manner of propagation and selection of 

 cuttings, yet this natural inherent constitution of each variet}^ is the 

 only explanation for the different degrees of susceptibility of different 

 varieties. 



Among the varieties which the writer has had under observation, 

 Uncle John, Alaska, Delia Fox, and McGowan as a rule proved to be 

 very sensitive to the punctures of not only aphides, but also to those 

 of thrips and red spiders. Vigorous plants of the variety Storm King 

 spot readily as the result of the punctures of aphides, but do not 

 appear to be otherwise injured much, while weak plants of this variety' 

 become badly stunted and lose many of their leaves. The same may 

 be said of Bridesmaid, Sweet Brier, Scott, Garfield, Davbreak, Meteor, 

 and Jacqueminot. Garfield and Daybreak are much more injured 

 by thrips than by aphides. Among the other species of Diauthus, 

 D. areiKiriiiS is particularly sensitive to aphis punctures, especiall}" 

 if the stem is much injured, in which case the plants often die. 

 D. fanatica^ D. caeslws^ D. chinensis^ D. atroben^^ and 1). 2>lu7ncmi(,s 

 are less sensitive, but spot readih' from punctures of aphides, thrips, 

 and red spiders. D. chinsnms heddeimg!! and its varieties, especially 

 the thin-leaved sorts, are particular!}' sensitive to the punctures of 

 aphides and thrips, and are quite sensitive also to the punctures of red 

 spiders. 



METHODS OF CONTROLLING THE DISEASE. 



As the result of their investigations, Arthur and Bolley recom- 

 mended that aphides be kept down as thoroughly as possible and that 

 particular care be taken not to wet the foliage in watering. These 

 recommendations were based on their theory that the aphides serv^e 

 in a measure as carriers of the disease and that water facilitates the 

 development of the bacteria that were believed to be the cause of the 

 malady. 



There is much to commend in the methods of watering suggested 

 by Arthur and Bolle^^, and their efforts in stimulating search for 

 better methods of staking the plants so as to keep the foliage more 

 exposed to light and air have also resulted in much benefit. The 

 increased vigor resulting from the use of these improved methods, 

 however, was not due to a decrease in the number of spots, as was 

 first believed, but to the fact that the total injury resulting from 

 punctures was reduced. 



The genus Dianthus is adapted to dry situations,^ but all the species 



^Williams, F. N., Jour. Roy. Hort. Soc.-, 1891, Vol. XII, p. 464; Arthur and 

 Bolley, 1. c. 



