DISEASES OF CULTIVATED PLANTS 635 



ping of the injured leaves, and growth and flower production is 

 seriously interfered with. The young buds themselves are often at- 

 tacked by the mildew, the flower clusters of the Ramblers sometimes 

 being completely covered by it and entirely worthless. 



Cause of Mildeiv. If one of the very young mildew spots which 

 can just be distinguished is examined with a microscope which mag- 

 nifies 10 or 20 diameters, one can easily see that the spot consists of 

 a mold-like growth. This fungus is composed of slender, white 

 threads with numerous branches, running out from the center of the 

 spot and forming a net-work over the surface of the rose leaf. At 

 various points these threads produce a different kind of branches, 

 which are erect and bear on their ends chains of minute egg-shaped 

 bodies (spores) .which are easily detached and in older spots lie in 

 masses on the surface and give it a powdery appearance. (Md. E. 

 S. B. 156.) 



For greenhouse roses, keep the steam pipes painted with a paste 

 made of equal parts lime and sulfur mixed up with water. The 

 mildew is a surface-feeding fungus and is killed by the fumes of the 

 sulfur. Out-door roses that become infested with the mildew may 

 be dusted with sulfur or sprayed with a solution of potassium sulfide, 

 1 oz. to 3 gallons water. Spray or dust with the sulfur two or three 

 times at intervals of a week or ten days. (N. Y. [Cornell] E. S. B. 

 252.) 



The apparatus used for this work is called the Campbell vapor- 

 izer. In this the sulfur boils over an alcohol lamp but does not 

 burn. This is very effective and safe if the directions are closely fol- 

 lowed. The principal feature of this device is the pot in which the 

 boiling takes place. There being only a small opening in the top 

 of this vessel it is almost impossible for the sulfur to get on fire. It 

 must be watched, however, for it will sometimes, if quite full, boil 

 over. The vapors given off in this apparatus are entirely different to 

 those in which the sulfur is burned. Soon after the lamp is lighted 

 a rather heavy, yellow vapor rises from the mouth of the pot. This 

 seems to be composed of very fine particles of sulfur. After a few 

 moments this vapor begins to settle down all over everything in the 

 house. Thus all the foliage is covered with a fine layer of sulfur. 

 The effect on the mildew does not seem to be immediate, but after a 

 few days the grayish looking fungus disappears and nothing but the 

 black scars are left. 



The common method of painting the heating pipes with a 

 mixture of sulfur and a small amount of lime has a similar effect 

 on the mildew, but a much less dense vapor is seen. 



Maynard of Massachusetts reported in 1889 (Hatch Exp. Sta. 

 Bulletin 4) the successful use of volatilized sulfur for the control of 

 rose mildew, black spot and even red spider. He used a handstove 

 on which' the sulfur was kept heated to near the boiling point in a 

 thin iron kettle for 3 or 4 hours, 2 to 3 times a week, or enough to 

 give a visible vapor in the house, taking every precaution to prevent 

 burning the sulfur. A somewhat similar method is used by some 



