CLADOSPOPJUM DENDRITICUM. 431 



(5) The lower branches are more affected than 

 the upper, and the propagation of the parasite takes 

 place from the base to the summit. 



(6) Land too highly manured induces rust. 

 Among the occasional causes producing fungi 



are — 



(1) An atmosphere habitually charged with mois- 

 ture. 



(2) Absence of light. 



(3) Sudden changes in the atmosphere, as a tran- 

 sition from heat to cold, or from a dry to a moist 

 state. 



(4) Long-continued drought. 



(5) Crowded growth. 



(6) Plants with creeping stems. 



(7) Leaves soiled with earth, or other impurities. 



(8) Changes of climate, causing corresponding 

 changes in the development of the plant. 



(9) Liundation. 



Of Fungi, these kinds deserve special notice — 

 (1) Cladosporium dendriticiim. This fungus at- 

 tacks not only the leaves, but also the fruit of the 

 apple and pear. It completely exhausts the foliage, 

 spreading over it, and causing black spots which, 

 in the fruit, often produce cracks. Those caused 

 by fungus must be distinguished, however, from 

 those cracks caused by a sudden and superabundant 

 flow of sap. This fungus is very persistent, and 

 seldom leaves a tree in which it has once obtained 



