INSECT PESTS AND DISEASES 131 



tissues of the leaf, and in about one week's time pro- 

 duces another crop of ripe spores ready to* continue the 

 work of extending the disease. This explains the 

 rapid manner in which the disease spreads during the 

 uredo stage. 



"Later in the season, when the grower has lost all 

 interest in the diseased plants, the same mycelium of 

 the fungus which, during the earlier part of the season, 

 has bees producing myriads of summer spores, now 

 gives origin to an entirely different form of fruit called 

 'teleutospores,' or winter spores. These differ in form 

 from the uredo or summer spores in being formed of 

 two cells, and more especially in the fact that the 

 winter spores will not germinate and grow until after 

 a period of rest. They remain in a quiescent state 

 until the following spring, when they germinate and 

 produce minute spores, some of which find their way 

 on to the Chrysanthemum leaves, germinate, enter the 

 tissues of the leaf and in a short time give origin to 

 the uredo or summer condition of the fungus. The 

 continuance of the disease, therefore, is entirely the 

 result of plants becoming inoculated by the resting 

 spores produced by the fungus the previous year. Too 

 much care cannot be exercised in collecting and burning 

 all diseased leaves. A single dead leaf bearing teleuto- 

 spores is more than sufficient to secure a crop the fol- 

 lowing season. Potassium sulphide is an excellent 

 preventive, as this solution destroys germinating spores 

 before they pierce the cuticle and enter the tissues of 

 the leaf."" 



Professor Arthur of the Indiana Experiment 

 Station says : "A circumstance much in the cultiva- 

 tor's favor is the propagation of the disease without the 

 formation of the teleutospores. Not only does this 

 render the disease far less persistent, but, without doubt. 



