220 BOARD OF AGRICULTURE. 



or knots, in these three cases, resemble one another, it is not 

 because they originated from the same cause, but because, an 

 irritation of the plant-cells having arisen from different 

 causes, the cells themselves, first unduly stimulated, and 

 then exhausted, have assumed a morbid action somewhat the 

 same in the three cases before us. Now, to the fruit-raiser, it 

 is of the first importance to know the cause, the origin, of the 

 diseases on his trees, because that is necessary to a thorough 

 understanding of the reasons for adopting certain remedies, 

 or means of preventing the spread of the disease. The 

 origin cannot be guessed from a hasty inspection, as we see 

 in the three tumors on plum, blackberry, and hickory. To 

 decide the question, a microscojjic examination is generally 

 necessary, and often a long and tedious examination. 



We have just said that the swelling known as the "black 

 knot" is caused by a fungus. What is meant by a fungus? 

 Fungi are plants of a very low organization, which are never 

 of a grass-green color, and which are not capable of absorbing 

 inorganic matter, and converting it into nourishment for 

 themselves, but must take directly from other plants or ani- 

 mals the organic matter which has already been formed out of 

 the inorganic materials contained in the soil and the air. All 

 plants which are capable of changing inorganic into organic 

 material contain a quantity of green coloring-matter known 

 as chlorophyl, which is not found in fungi. Fungi are, in 

 the strict sense, parasites, and, not being able of themselves 

 to assimilate the inorganic materials about them, must appro- 

 priate it from other plants and animals as best they can : 

 consequently any plant which has a fungus growing upon it 

 inust not only manufacture food enough for itself out of 

 the surrounding earth and air, but enough also to support the 

 fungus. If enough cannot be provided for both, it is the 

 plant which must suffer, and not the fungus, which helps 

 itself without ceremony to any organic materials which it 

 wants. The more the fungus grows, the worse for the plant 

 on which it is growing. Fortunately for the world, the 

 different species of fungi do not all require the same substance 

 for their support. Some do not grow upon living animals or 

 vegetables, but only upon dead substances, and are useful, 

 inasmuch as they hasten the decomposition of bodies which 

 would otherwise slowly putrefy. The fungi which live on 



