Parasitic and Saprophytic Fungi in Orchards. 201 



mining atmospheric conditions. So this part of the work need 

 only be a confirmation of facts already known, and explanatory 

 of the presence or absence of particular forms at certain times. 



Of these three factors, whicli control the presence of atmos- 

 pheric spores, rain, snow, or precipitation of any sort, is the most 

 important in decreasing the total number in the air at a given 

 time. This can be accounted for in that those which are floating 

 in the air will be washed to the ground, as will those which are 

 adhering to the tree, or they may be held by the film of water 

 which surrounds the twigs. That the air is freer from organisms 

 after a rain than at any other time is a matter of common 

 knowledge. 



Wind has just the opposite tendency. Several investigators 

 have found this to be true as a result of their work. One has 

 shown the marked influence of air streams in the spread of spores. 



Bernbeck* shows this very clearly in his work on the wind 

 as a factor in plant diseases. 



The factor which would seem to be of least influence as 

 observed in this work is temperature. The following is a record 

 of the temperatures for November, December, January, February 

 and March: 



No. of zero days 



November ... 



December ... 



January 



February. ... 2 



March 



Minimum 



16° Fahr. 

 5° " 

 4° " 



—4° " 



14° " 



Sum of zero degrees 













 -4 on 1st 

 -2 on 2nd 







41 .8° 



This record shows rather a :rJld winter. While low temper- 

 ature does have a great influence upon some forms, yet all are 

 not aff'ected in the same manner. This has been shown in the 

 fact that Phyllosticta limitata occurred during this whole periods 



If an arrangement of these factors in the order of their im- 

 portance could be made, it would be rain, wind, and temperature. 



RESULTS AxND CONCLUSIONS. * 



The following are the most important conclusions which may 

 be drawn from the results of these glucose agar exposures in 

 the orchards. 



•Bembeck: Der Wind als Pflanzenpathologischer Faktor. (Diss. Bonn, 1907.) 



