244 AGRICULTURAL EXPERIMENT STATION. [Jan. 



spore threads may be quite .sparingly developed, so that 

 only a faint frosting is to be seen. In attacks of much 

 severity there is commonly a discoloration, followed finally 

 by the drying up of the tissues affected. As has been seen 

 above in our discussion of some diseases due to these fungi, 

 they are surface parasites. The whole fungus grows on the 

 exterior of its host, except the small absorbing organs, 

 which penetrate only the superficial cells. And this fact 

 makes it much easier to deal with these fungi than with those 

 which are truly internal parasites, since practically the 

 whole of the fungus is exposed to the contact and action of 

 any fungicides applied to the surface of the host-plant. 



It should not be necessary to insist upon the prime impor- 

 tance of healthy conditions, so rei^eatedly emphasized in 

 these reports, and it may be assumed that it is not necessary. 

 Supposing, then, that reasonable precautions against the 

 appearance of fungous disease have been taken, and that one 

 of the powdery mildews appears, what can be done? The 

 question may be discussed mider two heads, namely, What 

 can be done for plants in the greenhouse ? And for those in 

 the open air? If the disease appears in a greenhouse, either 

 of the applications to be recommended for out-of-door plants 

 may be used with equal success. But, if the house can be 

 tightly closed, we have at hand a simpler, and, from the tes- 

 timony of practical men, an even more satisfactory, means 

 of treatment. This consists in filling the air of the tightly 

 closed house with the vapor of sulphur, which is fatal to 

 these surface parasites, without injuring their host-plants, 

 if the exposure be not continued much beyond half an hour 

 at a time. After this treatment ventilators should be opened, 

 and the house given a thorough airing. The treatment may 

 be repeated whenever the reappearance of the fungus shows 

 it to l)e necessary. The sulphur vapor is easily produced 

 by heating the flowers of sulphur to a temperature some- 

 Avhat above its melting point, and kee})ing it at that i)oint as 

 long as desired. A porcelain-lined iron vessel for the sul- 

 phur and a small oil stove for heating constitute the entire 

 outfit needed for a small house. For a large one as many 

 such outfits may ])e used as are required to yield vapor 

 enough to saturate the atnios])hore of the room. Great care 



