NATURAL AND ARTIFICIAL INFECTION. 57 



advisable to lay portions of diseased leaves directly on healthy 

 ones, it is much better to place them near each other in a 

 moist chamber, hanging the former over the latter. 



When infection is carried on out-of-doors, it is best to obtain 

 a small plant which can be accommodated under a bell-jar. If 

 this be unattainable, it is often possible to bend one of the lower 

 branches down to the ground or other support, so that it can be 

 covered with a beU-jar. Again, a branch or portion of it may be 

 first sprinkled, then bound loosely up in a parchment-paper. 

 When carrying on infection it is of importance to avoid very 

 hot and dry or cold days ; moist, warm and cloudy days, or close 

 still nights, will be found best. In the case of diseases of the 

 rind, it is generally necessary to wound the periderm by a few 

 fine knife-cuts, then to place thereon a few drops of water with 

 infecting spores suspended in it. 



Artificial infection by means of mycelium is generally 

 attained by placing a diseased portion containing living my- 

 celium in contact with the healthy, so that the mycelium can 

 grow from the one to the other. Thus, with bark-diseases, a 

 small portion of diseased rind is cut out and fitted into a 

 corresponding incision in the rind of the plant to be infected, 

 the oculation or graft -being then protected against drying up by 

 gutta-percha, tree-wax, or parchment. The ingrafted portion 

 need not fit very accurately if well bound up, because the 

 mycelium will grow well in the moist chamber so formed. The 

 most vigorous mycelium is generally found on the boundary be- 

 tween healthy and diseased parts, so that portions from this 

 region should be selected for infection. 



If the fungus under investigation frequents the wood, it is, as 

 a rule, a wound-parasite, so that for its infection the wood must 

 be laid bare, and a diseased portion applied to it. If a branch is 

 to be infected {e.g. with Nectria, or Cucurhitaria), then it should 

 be cut over a bud, the exposed end split, and a fine wedge of 

 diseased wood inserted, the whole being bound up. It is also 

 possible to graft a diseased branch on to a healthy. In the 

 case of stems, a portion of the healthy one should be removed, a 

 diseased piece inserted, and the wound closed over with grafting- 

 wax or clay. Pressler's growth-borer may in such cases be 

 used with good results to obtain a cylinder of diseased wood, 

 and to make a suitable receptacle for it in the sound plant. 



