SYMPTOMS OF DISEASE IN PLANTS. 241 



to a deep-seated disturbance of the nutritive processes which results in 

 the decomposition of more or less extensive masses of tissue. Some of 

 the external factors which especially favor or predispose to this trouble 

 are heavy soils, high levels of ground water, deep planting, and trans- 

 planting at inopportune times. 



The rotting of parts or organs of plant, the "gangrene" of plant 

 tissue, is always due to the presence of some organism, either a fungus 

 or bacterium. In some cases there may be a slow decomposition of the 

 tissue without any liquefaction or softening of the affected parts. In 

 these "dry rots" the parasitic organism gradually digests cell-wall or 

 reserve food materials or both, with the result that living cells are 

 deprived of their necessary food, and succumb or are directly attacked, 

 while mechanical tissues are weakened and fail to perform their normal 

 functions. In other cases the rotting may be fairly rapid, with more 

 or less liquefaction and softening and discoloration of the affected parts. 

 In these "soft rots" the fungus or bacterium generally spreads rapidly 

 through the affected parts in case favorable conditions prevail. 



There are no parts of a plant that are exempt from rotting, but in 

 general the dormant or languid parts are more likely to suffer from the 

 inroads of rot producing organisms. Nearly all the troubles in which 

 rotting is a characteristic symptom may be grouped under the head 

 of root rots, stem or trunk rots, bud rots, and fruit rots. 



Plants with fleshy or woody roots often have their root system in- 

 vaded by parasitic or semi-parasitic organisms, which work in such a 

 way as to give rise to disease generally characterized as root rot. Woody 

 roots generally undergo such changes that the trouble is characterized 

 as a dry rot, while fleshy roots that are gorged with reserve food material 

 often of a saccharine nature are more likely to be affected by organisms 

 causing a soft rot. Our root crops, such as beets, turnips, carrots and 

 sweet potatoes, are often affected. Sometimes the organism that causes 

 the rotting gains an entrance while the roots are still growing in the 

 field or garden, and continues the work of destruction after the crop 

 is harvested and in storage. At other times the rot-producing organisms 

 only gain an entrance after the crop is harvested and in storage or 

 while the roots are in a dormant or languid condition and so less able 

 to withstand the attack. The soft rots of beets, turnips and carrots 

 are frequently due to bacteria, while the soft rots of sweet potatoes are 

 of fungus origin. Much can be done to prevent these troubles by proper 

 measures in the field and storage under conditions that are unfavorable 

 for the growth of either bacteria or fungi. 



Alfalfa or clover often suffer from root rots to such an extent as 

 to cause serious loss. In one such disease the affected field will show 

 small circular patches of dead plants which increase in circumference 

 as the fungus advances through the soil. In another case the dying and 

 dead plants are scattered throughout the field and show a rotting of 

 the root of a different character. The evidence at hand leads to the 



