92 POTATO DISEASE. 



sclmieder, and confirmed by Kubn and De Bary, botanists of Ger- 

 many. These investigators have not merely looked at the blighted 

 leaves and seen the fungus there, but have watched the fungus as 

 it rapidly sends out its branches into the still fresh and healthy 

 portions of the leaf, and litei'ally devours them, appropriating their 

 juices to its own nourishment, and leaving behind a disorganized 

 and decayed mass as the track of its desolation. It is easy to see 

 with the unaided eye, that the fungus travels over the potato leaf 

 hefore the blight. If the observer carefully regards one of the 

 brown blight-spots when the disease is spreading, he will see that 

 at its borders, and extending over upon the still green leaf, is a 

 forest of tiny mould-plants which cover the leaf with a greenish 

 down. This is the potato fungus, the Peronospora infesians, as it 

 is now botanically designated. 



The manner of growth of this plant must be known before one 

 can understand its effects. It comes from a seed or spore of micro- 

 scopic dimensions, a minute, oval, somewhat flattened body, which 

 bears at either extremity a hair-like prolongature. These spores 

 are produced to the number of 12 — 16, together, in a spore-sack at 

 the extremity of a branch of the fungus. They are kept in a pecu- 

 liar rapid motion by the vibration of the hair-like appendages, and 

 when ripe they burst the spore-sack and are discharged. Their 

 motion continues about half an hour, when it becomes slower and 

 shortly ceases. Then the spore begins to change its figure, the 

 hairs disappear, and shortly a thread-like branch begins to protrude 

 from its side ; this rapidly increases, and if the spore is upon the 

 potato plant, the branch, which is the seedling fungus, so to speak 

 penetrates the tissues of the potato, — leaf, stem or tuber as the 

 case may be, — and forthwith commences its parasitic life. The 

 young fungus buds out in various directions, sending into the 

 juices and cells of the potato, its feeding branches or mycelium ; 

 while other, or fruit branches, pass out into the atmosphere, and 

 reproduce spores with marvellous fecundit5^ The growth of the 

 mother plant continues as long as it finds food, and the requisite 

 warmth and moisture. When the supplies existing in one place 

 are exhausted, the plant dies in that spot ; but the branches, which 

 had previously extended into the neighboring regions, continue to 

 grow, so that the devastations of this fungus arc like a fire which 

 spreads in all directions wherever it finds fuel. 



Nothing can explain the fact that a field which yesterday was 



