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Halsted : MvcoLOGiCAL Notes 



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the weed. There is a very striking difference between the normal 

 and the infested plants that renders it an easy matter to distinguish 

 them. The smutted specimens, invariably the whole plant, are 

 much more leafy and the inflorescence rarely comes to view, but 

 remains as a plump mass of black spores inclosed by the upper- 

 most leaves. 



One of the points of interest connected with the smutted Pani- 



cum is the fact that it remains green long after the healthy plants 

 have turned brown or lost their leaves. In going over a field 

 covered with the crab grass in late October the smutted plants are 

 quickly detected by the profusion of leaves of a deep green color. 

 Such plants often send out new roots at the joints, as if making a 

 desperate attempt at fruitfulness in spite of the smut that changes 

 each flower cluster into dusty spores as soon as it is formed. 



From the nature of the smuts generally and the observed facts 

 in this case, it is probable that the infection takes place while the 

 plants are quite young and the fungus afterwards infests all por- 

 tions. 



Early in the life of the plant the habit of growth is changed, 



and the fungus reaches the full fruitful condition before it is visible. 

 It is only in the advanced stage of the disease that the mass of 

 spores comes to view by the separation of the leaf bases that pre- 

 viously hid it from sight. In the normal plant the stem elongates 

 and carried up the forked inflorescence, but here the stem remains 

 short with its tip inclosed within enlarged leaves that are of darker 

 green than the healthy plants. This same dark green is charac- 

 teristic of the turnip plant that is having its roots destroyed by 

 the club-root fungus— a very conspicuous shade of green to those 

 who recognize it. 



'clop 



Host Immunity f) 



In a recent collecting tour it developed by inspection that the rust 

 Puccmia mamillata Schrt., while common upon the ordinary plants 

 of the climbing smart weed {Polygonum dumctorum L.) it was 

 nearly absent from all those infested with Ustilago anomala J. 

 Kunge. It would seem that the smut had taken possession of the 

 plant and the latter did not longer furnish the proper feeding 

 ground for the rust. The same thing was found true in case of 

 the smutted specimens of Panicum sanguinale L., the leaves of 



