SYMPTOMS OF DISEASE IN PLANTS. 239 



elevation of the scab patch or in the deep form there may be more or 

 less corrosion and destruction of tissue. 



The so-called crown-galls which may be called our "vegetable cancers" 

 are due to the stimulating effect of some organism in the majority of 

 cases. In these cases irregular, abnormal enlargements appear at the 

 crown or even upon some of the roots as in the raspberry, blackberry, 

 grape, peach, apricot and apple. The club-root or finger-and-toe disease 

 of the cabbage and other cruciferous plants should also be included in 

 this category. 



The name "canker" is applied to a malformation in the bark of trees 

 which generally results in an open wound. In the younger stages of 

 a canker the bark may be only slightly different from the normal, some- 

 times being sunken, sometimes showing a more tumid condition. The 

 canker area may also show differences of color and with the advance 

 of the disease the bark becomes roughened and begins to break and 

 peel away. The destruction of the cortex or bark may thus leave an 

 open wound which exposes the wood, while the parasite itself penetrates 

 the wood deeper and deeper or other wood-rotting fungi gain an entrance 

 and help to complete the destruction. There are at least six different 

 canker-producing fungi which grow upon apple trees. The same organ- 

 ism which produces the canker may also cause a rotting of the fruit. 

 This is true in the bitter-rot canker, the black-rot canker, and the 

 Pacific-coast canker, all of which occur in this state, while the organisms 

 which cause European canker, the Illinois apple-tree canker and fire- 

 blight canker do not attack the fruit. In some cases open wounds on 

 trees due to sun-scald may be confused with cankers due to fungi, but 

 in general a careful observation of the location will reveal the difference. 

 Canker-producing fungi, however, may enter sun-scald wounds and con- 

 tinue the destruction. A bacterial canker of plums has been observed in 

 this state especially upon two varieties, the Wickson and Whitaker. 

 These plum cankers are on the smaller branches and are produced by 

 radial fissures in the bark which make more or less open wounds, due 

 to the destruction of tissues and the relief of the transverse tension. 



It is not uncommon to find upon the trunk or limbs of forest, orna- 

 mental, or orchard trees the fruits or sporophores of some of the higher 

 fungi. Some of these common forms are toadstool-like in appearance, 

 while others are in the form of brackets, the so-called bracket fungi. The 

 latter are often called "punks" or "conchs" by lumbermen and foresters. 

 Some of these higher fungi only grow in wood or branches that are dead 

 or in a languid condition, while others gain an entrance through open 

 wounds into healthy limbs and begin the work pt destruction, while still 

 others are more virulent and do not require either of the above condi- 

 tions. In general, these fruits of fleshy fungi upon a woody plant may 

 be considered indicators of disease, and they should be destroyed as 

 soon as they appear to prevent the spread to other trees. The wood 

 of a tree is always well pervaded by the vegetative body of the fungus 



