34 BOARD OF AGRICULTURE. [Jan. 



it attacks. The disease is propagated by reproductive or- 

 gans known as spores, which are analogous in their function 

 to the seeds of the higher plants. This plant is one of the 

 thousands and thousands of so-called fungi, which constitute 

 a very large brood of small, largely microscopic plants, 

 which attack either dead and decaying plants and animals, 

 or living plants. Those which attack living plants, like the 

 black-knot fungus, are known as parasitic fungi, because 

 they live on and at the expense of the plants which they 

 attack, drawing their nourishment from them ; having no 

 power of elaborating nourishment for themselves, as the 

 green plant, a plum tree, for instance, has, but depending 

 entirely upon the nourishment elaborated by the plum tree 

 for its food. The reproductive organs or spores are very 

 small in all the fungi, microscopic in size, and so naturally 

 very light. They are readily carried by the v/ind and by 

 very slight currents of air. The early history of the de- 

 velopment of the black-knot fungus we do not know. We 

 do not know definitely how it first penetrates the branches ; 

 we can judge of that only from its analogy to other fungi. 



The spores presumably infect the branches of a plant by 

 producing little germinating threads which grow out from 

 the spore and push their way, you might almost say dissolve 

 their way, perhaps by some chemical action on the surface 

 of the branch, into the interior of the branch, through the 

 dead cells of the bark into the living, active cells of the 

 new wood, living at the expense of the nutritive material 

 which has been elaborated by the plum or cherry tree. The 

 body of the fungus is composed, like the body of all the 

 fungi, simply of little whitish, nearly transparent threads, 

 microscopically small, Avhich ramify in all directions through 

 the tissues at whose expense the fungus is growing. The 

 interior of any of the cells, when examined through the micro- 

 scope, shows plainly these branching, ramifying threads. The 

 swelling, which gives the name " knot" or " wart," is due, 

 undoubtedly^ to an abnormal stimulation of the branch by 

 the fungus growing into it. The cells of the young wood, 

 which are the active, living cells of the branch, increase and 

 multiply very largel}^ and you have a large, stout, suc- 

 culent knot in the early stages. That knot becomes a mere 



