FUNGOUS DISEASES 



7 



important of the contact poisons and pyrethum or 

 insect powder is a good example of a tracheal poison, 

 although the various vapor insecticides, like carbon 

 bisulphide and hydrocyanic acid gas, also belong here. 



DEVELOPMENT OF PARASITIC FUNGI 



Many other instances of the usefulness of the 

 spraying machine in controlling noxious insects will 

 be found on the later pages of this little book. To 

 illustrate the theory of its use against the fungus 

 enemies of crops, as well as the life history of the 

 parasitic fungi themselves, we may instance the 

 Doz^iiy Mildezx', which causes the Brown Rot of 

 grapes. 



The Brown Rot of grapes is a fungous disease — 

 that is, it is a diseased condition of the foliage or fruit 

 due to the presence of a fungus. This fungus is a 

 minute, parasitic plant that develops at the expense of 

 the tissues of the grape, thus causing blighting of the 

 leaf and decay of the fruit. It attacks all the green 

 parts of the vine, including the young shoots, as well 

 as the leaves and berries ; and, like other fungi, repro- 

 duces by means of spores — ^^minute bodies correspond- 

 ing in function to the seeds of flowering plants. 



When one of these spores falls upon a moist leaf 

 its contents divide into a number of distinct particles 

 which escape through an opening in the spore-wall. 

 Each of these particles moves about in the drop of 

 water on the leaf for a few minutes, then comes to a 

 standstill and germinates by sending out a little tube — 

 somewhat as a kernel of corn in moist soil sends out 

 its germinating radicle — and this tube penetrates the 

 epidermis or skin of the leaf. Once inside, the tube 

 continues to grow, pushing about between the cells of 

 the leaf, and forming what is called the mycelium or 

 vegetative portion of the fungus, which may be likened 



