632 COMMON DISEASES OF PLANTS 



It may be used in a water solution, at a strength of about 1 oz. to 

 6 gallons of water. For books, specimens, etc., the following 

 proportions are recommended : corrosive sublimate i oz., carbolic 

 acid i oz., methylated spirits 1 pint ; apply with a soft brush. 



SOME COMMON DISEASES OF PLANTS 



Club-root or Slime Fungus. This disastrous fungus disease 

 attacks the roots of all plants of the Cabbage family (see under 

 Cabbage), and does a great deal of damage in up-country gardens, 

 rendering them in many cases unprofitable for cultivation ; it 

 produces large nodules on the roots and, the leaves becoming 

 yellowish, the plants suddenly die. The disease spreads readily 

 by means of spores carried on implements or with plants trans- 

 ferred from an infected area, and once established it is impossible 

 to eradicate it, except by giving up the cultivation of Cruciferous 

 plants for two or three years. Fresh unslaked lime, applied at the 

 rate of 75 bushels to the acre, or about 15 Ib. to 100 sq. feet, will, 

 however, check the disease considerably for a time. Rotation of 

 crops also minimises its effects. 



Sooty Mould. Orange trees and other members of the Citrus 

 family are peculiarly liable to this fungus disease, which forms a 

 black crust on the foliage, sometimes covering the entire leaf, and 

 occasionally blackening the fruits also. It is, however, a super- 

 ficial growth and does not penetrate the tissues of the plant. Its 

 presence is due to scale-insects (species of Lecaniiini), which must 

 be got rid off in order to effectually dispose of the mould. Spray- 

 ing with petroleum emulsion or a resin wash, followed by syringing 

 with clean water, is the best remedy. The scale-bug (Lccanium 

 hemisphcericum) is a very common pest on ferns and other 

 pot-plants, while Lecanium viride or green-bug is often trouble- 

 some on oranges, coffee plants, etc. 



Gumming, or Gummosis. This condition, which sometimes 

 occurs on fruit trees, especially on Oranges and other Citrus trees, 

 is usually induced by badly drained soils or external injury, as 

 through improper pruning. Experts are not, however, agreed 

 upon the actual cause of the disease, which has been attributed to 

 fungi or bacteria: but it is a common result of injury to the cam- 

 bium. The best way of preventing its occurrence consists in 

 affording the trees proper cultivation, and preventing as far as 

 possible any rupture of the bark. A remedy that sometimes proves 



