Apr. 3, 1916 



Climatic Conditions and Cercospora beticola 



39 



cated on diagrams. As new leaves developed, they were included in the 

 observations, and this was true also of new spots, until they became too 

 numerous, after which only a few representative ones on each leaf were 

 studied in detail. During the period from the 24th of June to the 19th 

 of September 330 spots were studied, both surfaces being examined at 

 frequent intervals with a hand lens. For the purpose of getting a basis 

 for comparison of rates of development at different stages in the life 

 history of the disease, percentage values were assigned to each stage as 

 follows, the spots being grouped and averaged later (Table IV) : 



Percentage value. Stage of development of fungus. 



5.0 Spot first noticed. Neither conidia nor conidiophores present. 



12.5 Conidiophores present. 



19.7 Very few conidia. 



25 Few conidia. 



31.2 Conidia fairly numerous. 



37.5 Conidia numerous. 



43.7 Conidia fairly abundant. 



50 Conidia abundant. 



The value of the spot is the sum of the values of the two sides— ^that 

 is the value of a spot on which there were but few conidia (25) on one side, 

 and abundant conidia (50) on the other, is 75. Again, the value of a 

 spot on which conidiophores only (12.5) were present on one side, and very 

 few conidia (19.7) on the other, is 32. '^ 



Table IV. — Data on life histories of a representative number of leaf spots studied on 

 10 plants in a medium-early sugar-beet field near Rocky Ford, Colo., during the season 

 of 191 3 b 



o For convenience the decimal fractions, which make only a negligible difference in the averages, are 

 omitted. 



<> In Table IV asterisks (*), daggers (t), and section marks (§)are used to designate definite leaf spots 10 

 which reference is made in the text. 



