16 DISEASES OF FIELD & GARDEN CROPS. [CH. 



freshly-cut sets in the soil immediately after cutting, and 

 whilst the wound is still quite fresh. Planting in rank 

 undecayed material is not only destructive to the material 

 which is stored up within the tuber or set (material 

 which is the food of the future plant), but it is also in- 

 jurious to the young shoots and rootlets, for any hot, 

 fermenting material acts as a poison to these growths, and 

 diminishes the vigour of the infant plant. The conditions 

 of planting in the instance here adverted to may, how- 

 ever, have had nothing to do with the disease which 

 followed in the summer. 



Until the attack now under description, the potato 

 plants, as far as outward appearances went, were free from 

 any taint of the fungus of the potato disease proper, 

 named Peronospora infestans, Mont. The disease was first 

 noticed in the beginning of July, at the time the potato 

 flowers were opening ; but there can be little doubt that 

 it was in or upon the plants several weeks previously, as 

 by its nature it would not attract much attention at first. 

 It is strange that other potatoes named " Protestants," 

 growing close to the " Champions," were not attacked. 

 The appearance of the diseased plants was peculiar ; they 

 were covered within and without with a thick felt of 

 white fungus spawn or mycelium. The growth of this 

 spawn was so rapid and profuse that in a week or two the 

 whole of the stems and leaves were reduced to tinder, the 

 entire moisture belonging to the stems and leaves being 

 exhausted by the fungus. Leaves are of such vital im- 

 portance to plants that the destruction of them is 

 synonymous with a cessation of the plant's growth. If 

 the parts of a potato plant which are above ground get 

 seriously injured or destroyed, there will be little or no 

 further growth in the tubers. In the Peziza disease, now 

 under description, the mycelium was not a putrefactive 

 one as in Peronospora. It merely caused a sudden cessa- 

 tion of growth in the tubers. 



Immersed in the thick felt of white fungus spawn, 



