222 AGRICULTURAL EXPERIMENT STATION. [Jan. 



high a night temperature is probably a common cause of the 

 rapid progress of the disease. All diseased plants and all 

 refuse on which the fungus can live and increase should be 

 removed at once from the greenhouse and burned. For this 

 purpose the boiler furnace is conveniently at hand. Every 

 bit of vegetable remains should be often and scrupulously 

 cleaned up and destroyed. A house which has been badly 

 infested by the disease should be thoroughly cleaned, fumi- 

 gated with burning sulphur and supplied with fresh soil, 

 before a new season's crop is started. A coat of paint or 

 whitewash over the whole interior may also be a useful pre- 

 caution. With a hduse thus disinfected and a crop well 

 nourished and well cared for, one may legitimately expect 

 practical freedom from loss by rotting. 



The Powdery Mildew of the Cucumber. — EnjsipJie 

 cichoracearum DC* 



So far as I know, the first announcement of a powdery 

 mildew on cucumbers, in America, was made in Bulletin No. 

 40 of this station in August last. It has long been known 

 in Europe and has been observed in Australia. It is not 

 known to me to attack cucumbers cultivated in the open air, 

 but is probal^ly not uncommon on plants forced in the green- 

 house for a winter crop. It has been sent to this department 

 by Dr. Jabez Fisher of Fitchburg and by Prof. L. H. Bailey 

 of Cornell University, Ithaca, N. Y. 



The disease ordinarily first appears on the upper surfaces 

 of the leaves, and sometimes on the stems, of the host-plants, 

 in the form of small, roundish, white spots, which have the 

 peculiarly powdery appearance which has given to this group 

 of fungi their name. These young spots suggest the effect 

 of scattered splashes of flour upon the plant. Microscopic 

 study shows that the white substance consists of the threads 

 and spores of the parasite. The surface of the host-plant is 

 covered b}'" a close layer of flattened cells, the epidermis, 

 and the vegetative threads of the parasite develop close to 

 this outer surface. They are thus truly external, instead 

 of ramifying among the internal cells of the host, as is the 

 case with the cucumber mildew described in the last report 



* See note, p. 219, 



4 



