DISEASES. 15 



them. Pruning may be done at any time, but preferably when the 

 atmosphere is dry, so that the cut surface may dry and heal quickly. 

 In conservatories during the colder season, in order that the air 

 may be sufficiently dry, a temperature ranging from 60° to 70° F. 

 should be maintained. A temperature lower than 60° for any con- 

 siderable length of time would hold the moisture about the plants too 

 long and invite decay. During the warmer season, if the plants are 

 kept in the house it is necessary that it be kept fully ventilated. 

 The aim is to have at all times a dry atmosphere and a moderately 

 moist well-drained soil. If the plants are placed in open ground during 

 the summer months and their pots plunged in the beds, these beds 

 likewise must be thoroughly drained. In placing a collection out of 

 doors as a permanent planting, a situation should be selected, if 

 possible, where the ground slopes sufficiently to insure perfect drain- 

 age. If natural drainage is impossible, a system of drain tiles should 

 be placed throughout the area to be planted and the soil above the 

 tiles should be made loose and porous by the abundant addition of 

 gravel and sand. Out-of-door planting is preferably done during 

 the dry season, so that the cut surfaces or any injured portions of the 

 plants will dry over quickly and be less easily infected with rot. 



DISEASES. 



The one disease from which cacti suffer more than any other is 

 rot. The plant body is so saturated with water that it forms an 

 excellent medium for the growth of this disease. It is liable to attack 

 the plant at any point where the germs have opportunity to reach 

 the interior. Any cut or bruised place presents the most favorable 

 point for infection, from which the disease rapidly spreads and 

 destroys the plant. Water dripping on a plant for even a short 

 time may induce infection. By far the greater number of plants 

 receive the infection through their bases or roots, whence it works 

 upward through the center of the plant. By the time it has reached 

 the surface the plants are usually too far gone to be saved. If the 

 disease is detected before it has reached the crowns of the plants, 

 they may be saved by cutting away all the diseased portions and 

 then grafting the crowns on some healthy stock. Otherwise, it is 

 best to remove the plants at once and burn them. The soil in which 

 they were potted and also the pots, if to be used again, should be 

 sterilized, so that other plants may not be infected from them. 



Another disease more common to species of Mamillaria and to a 

 less extent found on Echinocactus and Cereus makes its first appear- 

 ance as a small, light orange-colored spot on any portion of the plant 

 surface, usually starting at a pulvinus, which seems to be the point 

 at which the infecting germ enters. This spot steadily grows until 



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