Nature of Plant Diseases loi 



will shake out the pollen and enough of it will be 

 liberated by this operation to insure complete fertili- 

 zation. A high temperature will favor the maturing 

 and the bursting of the pollen sacs even during 

 cloudy weather. It is, therefore, advisable to run 

 up the temperature of the house as high as is ex- 

 pedient on the days when the tapping of the blos- 

 soms is done. This should always be done during 

 the day and never at night. The pollen sacks (an- 

 thers or male organs) do not burst freely until after 

 the yellow petals have fully expanded and have 

 begun to wither slightly. The pollen is discharged 

 most freely in a hot dry atmosphere. 



3. Diseases Brought About by Parasitic 

 Flowering Plants or Micro-organisms 



In this class of diseases may be mentioned those 

 which are induced by parasitic flowering plants such 

 as the dodder and the broom rape. These, however, 

 as well as the diseases induced by bacteria and fungi, 

 will be considered under their respective hosts. 



Carriers of Diseases. In the greenhouse, dis- 

 ease producing organisms are often brought directly 

 with infected soil or manure in the compost. Fusa- 

 rium lycopersici Sacc, the cause of sleeping sickness 

 of tomato, as well as large numbers of other para- 

 sites, are brought in that way. 



Little as yet do we realize the importance of in- 

 sects as carriers and disseminators of plant diseases, 

 although we are becoming increasingly aware of 



