456 DISEASES OF ECONOMIC PLANTS 



houses. Though widely known in Europe, it did not seem 

 to be especially destructive there ; but upon entrance into 

 America its character changed to that of an aggressive pest, 

 and ruin was brought to the beds in many greenhouses. 

 The entire contents of large houses valued at thousands of 

 dollars was in many instances utterly lost. After a short 

 period of extreme destructiveness, which was at its height 

 about 1893, the vigor of the attack waned, until to-day the 

 pest does only a small fraction of the damage that was com- 

 monly due to it in the early years of its invasion, though it 

 is still one of the serious carnation diseases. 



The rust is easily recognized by the sori ; in this case full 

 of brown spores which may be rubbed out as a dark dry 

 powder. The sori, at first covered by the white epidermis, 

 are 1-2 mm. in diameter, round or elongated in the direction 

 of the length of the stem or leaf. When very numerous, the 

 affected part is slightly bleached or yellowed and appears 

 swollen, owing to the much-ruptured epidermis. The my- 

 celium of the causal fungus is usually general throughout 

 affected plants, but may, in case of new infection, be limited 

 to the immediate region of the sorus. 



There is much difference in varietal resistance, a fact that 

 should receive due weight in the selection of varieties for 

 culture. The William Scott is highly resistant. Uncle 

 John, Daybreak, Silver Spray, and Jacqueminot are 

 susceptible. 



Cuttings should never be taken from diseased stock. 

 If there is doubt as to the absence of superficial spores, it is 

 well to dip the cuttings in potassium sulphide, one ounce 

 to one gallon. A weekly protective spray of copper sul- 

 phate, one pound to twenty-five gallons, throughout the life 



