COMMON DISEASES OF PLANTS 633 



effectual is cutting out the affected part, and tarring the area or 

 covering it with cow-dung and clay. An application of Bordeaux- 

 paste (2 Ib. copper sulphate, 2 Ib. unslaked lime in i gallon water), 

 applied by a brush, is also recommended. 



Damping-off disease. The common malady known as 

 "damping-off " is due to a fungus (Pythium), which affects young 

 and small tender plants, especially seedlings from thickly sown 

 seed. It usually attacks the plants at a joint just above the ground 

 level and, the tissues becoming destroyed, the plants fall over from 

 that point. Excessive dampness, absence of light or ventilation, 

 and imperfect drainage are conditions which are conducive to the 

 disease. 



Dry-rot fungus. The disease known as "dry rot" (Merulius 

 lacrynians) frequently attacks timber in bungalows or other buildings 

 in the tropics. Soaking or spraying the wood with a solution of 

 formalin or other fungicide, at intervals of a few days, is said to be 

 the best preventive. 



Chlorosis in Plants. The disease called Chlorosis, which 

 means pallor or "green sickness," is not caused by a fungus or 

 insect pest, but by a deficiency of iron in the food of the plant. 

 It is noticeable by the foliage or other actively growing 

 part assuming a blanched appearance, the usual green colouring 

 matter (chlorophyll) being lacking; for without iron no chlorophyll 

 can be formed. It is not a serious or very common disease, and 

 can usually be cured by adding a weak solution of iron salt 

 to the soil. 



Fasciation (from "fasciculus," a little bundle). The primary 

 cause of the phenomenon known as fasciation which affects many 

 families of plants, is largely a matter of conjecture. It may occur 

 in the stem (as often seen in young Hevea stems), as a flat- 

 tened growth instead of the normal cylindrical stem; or in the 

 flowers, as in the Cockscomb and often in Roses; or in the fruit, as 

 frequently in Pine-apples. Some genera are more liable to it than 

 others, and in some cases it is hereditary, as in the Cockscomb 

 (Cclosia cristata). Fasciation is believed to be usually the result of 

 either of two causes, viz: (1) local injury to the plant whether 

 caused mechanically or by insects (gall mites being a frequent 

 cause), and (2) excessive nourishment (hypertrophy), i.e. overfeeding 

 of certain parts of the plant, which disturbs the equilibrium of 

 growth. 



