DISEASES OF PLANTS. 147 



literally devours them, appropriating their juices to its own 

 nourishment, and leaving behind a disorganized and decayed mass 

 as the track of its desolation. The fungus comes from a spore 

 which is oval and somewhat flattened, and bears at each extremity 

 a hair like prolongation. These spores are produced to the 

 number of 12-16, together in a spore sac at the extremity of a 

 branch of the fungus. They are kept in a peculiar rapid motion 

 by the vibration of hair-like appendages, and when ripe they burst 

 the spore sac 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, so to speak, the seedling fungus, 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 fecundity. The growth of the parent plant 

 continues as long as it can find 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 are like a fire which spreads in all 

 directions where it can find fuel." Professor Johnson, to whom I 

 acknowledge my indebtness for these interesting facts, has satis- 

 fied himself that where this fungus is there is potato disease, and 

 where the potato disease is there is this fungus. The connection 

 between the two, as cause and efiect, is beyond all question, and 

 it is idle to ignore the relation. The various remedies proposed 

 for this disease need further trial, and I forbear at the present time 

 to present any of them. 



We are thus brought to the consideration of the last class of 

 diseases, comprising all those produced by improper and insufii- 

 cient plant food. 



A plant may be poisened, starved or stuffed. Plant poisons are 

 very numerous. They may be said to be innunjerable. They may 

 float in the air as noxious gases, or they may be carried by the air 

 as solids in a state of fine subdivision, or they may be applied to 

 the plant through the medium of the soil. In manufacturing 



