526 STATE HORTICULTURAL SOCIETY. 



If any one will take the trouble to look at the year-old twigs of most trees 

 and shrubs, he will readily find in the bark little light-colored rough specks. 

 These are known to botanists as lenticles, and consist of cork-like formations, 

 the cells of which soon lose the power of absorbing water, and of course die. 

 They are, however, normal growth, and cannot be classed as disease products. 

 They likewise occur on the potato tuber, which is worth the while to remember, 

 it is a true branch of the stem, and in this respect is like ordinary aerial 

 branches. But it is claimed that, under some circumstances, these lenticles are 

 beginning points of rupture and decay in the skin, and that the final result of 

 this is the scab, without the intervention of any living external agent. Too 

 much water and too much nitrogenous manure are the principal causes given 

 for the cork-like development. The disease is certainly worse on rich and wet 

 land. 



So far as known, the depressed, rough spots on potato tubers, usually called 

 scab, are the result of normal growth carried to an excessive and destructive 

 development through surroundings adverse to the potato, and there is nothing 

 of a contagious character in the malady. The scab on the seed cannot, in this 

 view, affect the next crop. The difference in the structure of the skin of the 

 different varieties, is quite enough to account for the facts noted in the letter 

 of inquiry. 



Fungus Diseases. — Dr. Halsted speaks of the popular notion of fungus 



diseases as follows : 



Some people are quite sure that all of the various rusts, smuts, etc., are 

 caused by hot and moist weather. If we did not have frequent showers when 

 the wheat is "in the milk," we should have little or no rust. This is all 

 true, and the relationship between the rusts, etc., and the conditions of the 

 weather is easy to see. All forms of vegetation are dependent upon favor- 

 able conditions for their development. The wheat crop would be small 

 without sufficient heat and moisture. The rusts need, especially, these 

 last-mentioned conditions, and when they are right, growth of the rust 

 plants is very rapid. A few days ago I made a " culture " for some moulds 

 of the more common sorts, by using bread, sliced boiled potatoes and a little 

 meat, all moistened and placed in a warm place. In less than a week the 

 viands were entirely obscured from view by the forest of moulds covering 

 them. The various smuts, mildews and rusts growing upon plants are very 

 rapid in their development, and on this account it has been natural to con- 

 sider the conditions for their growth the reasons for their existence. The 

 warm rains and hot sun rusts the grain only in the sense that they provide 

 the favoring conditions for the development of the rust plants that feed upon 

 the nourishing fluids and change them into millions of orange-colored spores. 

 As well say that the same conditions are the cause of corn. They favor the 

 development of the corn crop, but the seed needed to be placed in the ground 

 before any harvest could be hoped for. It only remains to show why it is 

 that some sorts of grain, for example, are less rusted than others growing 

 alongside. This is as difficult as to show why one sort should differ from 

 another as they grow side by side. There is the same soil, the same rains, 

 the same sun, etc., and yet the sorts are distinct. If they are distinct as to 

 outward form, it is reasonable to infer a difference of vitality that is the 

 origin of all these outward differences. It may be that one sort of wheat 

 does not furnish the particular form of nourishment desired by the rust 



