Entomological Xotes. 



313 



and in producing them, the threads undergo a variety of changes, 

 some of which are very complicated. There are no true seeds or 

 flowers in fungi, but in their power of germinating and reproduc- 

 ing the species from which they were derived, the spores of fungi 

 correspond to the seeds of higher plants. Unfortunately for the 

 easy understanding of the subject, the mode of production of the 

 spores is a difficult subject to follow, and it is made more difficult 

 by the fact that many, perhaps most, fungi produce more than 

 one kind of spore, a state of things to. which we have nothing 

 directly corresponding in the higher plants with which we are 

 familiar. 



After this preliminary description of what is known as fun- 

 gus, let us examine the disease known as the " black knot." 

 The knots are most striking in the autumn and winter. If we 

 make a microscopic examination of a knot gathered in mid-winter, 

 we shall find that it is composed partly of a fungus and partly of 

 the diseased and distorted cells of the plum-stem. The white 

 threads of the fungus are found twisted together in bundles (Fig. 13 

 A),which in general are parallel to one another, and run from within 

 outwards. They extend down into the stem for a short distance 

 below the knot, but not more than a few inches. The threads in 

 the knot, as they come near the surface, branch more and more 

 and become black, and at the surface form a granular mass. The 

 granulations can be seen with the naked eye, and when examined 



under the microscope each granulation is 

 found to contain a cavity (Fig. 11), in 

 which are a number of sacs intermixed 

 with white threads. In the sacs are 

 eight spores (Fig. 12), each of which 

 consists of two parts, one being smaller 

 than the other. The whole cavity opens 

 outwards, and it is easy to see how the 

 spores reach the air. 

 When spring comes, the threads which were concealed in the 

 stem below the knot begin to grow again, and cause a new swell- 

 ing just below the old knot. In a few weeks they will have 

 grown to such an extent as to burst through the bark and appear 



Fig. 11. 



