124 THE PLUM IN KANSAS. 



formed within cavities in the substance of the fungus similar to those 

 in which those of the mature stage are produced. These are termed 

 stylospores. 



Some time during the summer the spores of the black-knot fungus, 

 which have found lodgment in the crevices of the bark of the trees, 

 germinate and push their germ -tubes into the cambium or growing 

 layer just underneath the bark, and the action of the fungus growth 

 upon the living cells of the cambium excite these into rapid and ir- 

 regular development, resulting finally in the production of the well- 

 known knots. By autumn the increased growth of the cambium is 

 often externally manifest as a slight swelling along the branches; 

 little change occurs during the winter, but in the spring following 

 the swellings begin to enlarge rapidly, and often attain their full size 

 in a few weeks. 



The bark covering the forming knots expands for a time with their 

 growth, but is finally burst asunder, exposing the diseased tissues 

 composing them. The fungus itself continues alive and active 

 throughout the summer and following winter, when the spores of the 

 mature stage, referred to above, are produced, after which the parasite 

 dies, and there is left a mass of open, dead tissues which offer protec- 

 tion and support to various insects that are likely to add to the injury 

 already occasioned. 



The fuagus of black-knot is remarkably well supplied with means 

 for reproduction, each spore produced being capable of developing a 

 new fungus growth and consequent "knot," if it falls under proper 

 conditions. To prevent this spread of the disease, we ought to remove 

 and destroy at once the knots wherever they may appear, both from 

 our orchards and from all wild trees that may be growing in the 

 vicinity. The knots on a single wild tree may yield spores enough 

 to infect the cultivated trees of an entire county. Badly diseased 

 trees of either sort should be cut down and the knots burned or other- 

 wise destroyed at once. When there is only here and there a branch 

 that is diseased, these alone may be removed with a saw or knife, the 

 knots destroyed, and the trees then disinfected by a thorough washing 

 with Bordeaux mixture, or, if the work be done in the winter, with a 

 very strong (30 to 50 per cent.) solution of sulphate of iron. These 

 solutions, if well applied with a strong force-pump, will doubtless 

 destroy or at least prevent the germination of any of the fungus 

 spores that may be resting on the bark awaiting suitable conditions 

 for development. The same solutions, if applied directly to the 

 newly developed knots, would probably prevent the formation of the 

 spores, but would not be likely to check the growth of the fungus 

 occupying the deeper tissues. The spread of the disease might thus 

 be prevented, but the injury then going on could not be checked. 



