534 



THE MONTHLY BULLETIN. 



ures are mere conjectures, based upon observation and theorj'. Oppor- 

 tunities for the propagation of the fungus should, if possible, be elimi- 

 nated. In this connection it might be suggested that no fruit be allowed 

 to remain on the trees or ground from one season to another to furnish 

 spores for the infection of the new crop. One infected orange may fur- 

 nish a million or more spores to be disseminated to the young fruit 

 in the spring. Other vegetable matter should not be allowed to rot in 

 or near the orange groves, as the fungus will propagate upon almost 

 any kind. 



Fig. 328. — (a) Half orange two months after inoculation with mycelium 

 from a pure culture of Alternaria citri. The cut surface and the peel is com- 

 pletely covered with a fungous growth and appears as a black smutty mass 

 with some whitish colored secondary mycelium over parts, (b) Half orange 

 inoculated as the above (a) and covered in the same manner, but cut in 

 two, showing that it is blackened throughout the interior as well as the 

 exterior, (c) Unaffected half orange shown as comparison with the above. 

 (Original.) 



Summary. 



1. Alternaria citri Pierce and Ellis, a fungus, is the cause of the 

 Black Rot of the Navel Orange. 



2. This fungus will propagate upon many kinds of vegetable mat- 

 ter and the conidia are disseminated to the blossoms or fruit (most 

 probably the latter) in the spring or early summer. 



3. This fungus is primarily a saprophyte but becomes a parasite if in- 

 troduced into the fruit. 



4. As it is very difficult to apply a fungicide in the navel of the 

 orange the advisable method of preventing infection seeins to be the 

 elimination of wintering over and breeding places of the fungus. This 

 means the destruction or removal of all decaying vegetable matters in 

 or near the orange groves. 



