lOO 



Journal of A^gricultural Research 



Vol. X, No. 2 



The needles of Douglas fir infected with this fungus in early winter 

 develop spots of a slightly yellow color on the under surface, principally 

 at their tips. Each spot represents a single infection and may be very 

 sharply separated from the unaltered green of the uninfected parts of the 

 leaf. Somewhat later the tissues of the leaf on the upper surface directly 

 opposite also turn yellow. By early spring (April and May) these spots 

 have changed to a yellowish brown, and since the uninfected parts of the 

 leaf may remain wholly green, merging into a Hght-yellow zone next to 

 the area of infection, a peculiar mottled appearance results. About the 

 first of June the needles have assumed, in the case of 

 severe infection, a more uniform brown color, and the 

 entire stand looks as if it had suffered from a severe 

 frost. On the under surface, on either side of the mid- 

 dle nerve of the needle, the spots, now dark brown, 

 begin to round up as small cushions. About the mid- 

 dle of June the epidermis covering these brown areas 

 ruptures with an irregular slit exposing the brownish 

 disk (fig. i). In cases of severe infection the needles 

 have a very striking appearance (PI. 12, A). At this 

 stage asci in all degrees of development are present 

 (fig. 2). Very frequently, if the tree has been much 

 suppressed by the destruction of its needles through sev- 

 eral seasons, mature spores are abundant. By July i 

 the asci (fig. 3) are fully mature, and sporulation is 

 active. The Hberation of the spores is very greatly 

 promoted by the force of wind and rain on the leaf. 

 When the spores fall on the young needles of the season, 

 which at this period are rapidly growing, it is observed 

 that infection takes places shortly afterwards, provided 

 sufficient moisture is present. 



Snow does not promote the spread of the fungus, as 

 shown by the fact that the needles of the branches of 

 the crowaare as badly infected as those lower down. If 

 a wet summer follows the infection, the needles begin to show signs of 

 being diseased before October; otherwise they will remain apparently 

 healthy until December. 



The infected needles fall at all seasons of the year, owing to the fact 

 that a portion of them are not as seriously infected as others and may 

 remain on the tree for an indefinite period. A slight jar is often sufficient 

 to cause the needles to fall in a shower. Those that remain longest on 

 the tree after infection produce the apothecia in the spring. In case of a 

 very severe infection, owing to the rapid drying out of the twigs, the 

 needles may remain indefinitely attached, the apothecia becoming black 

 and shrunken. Trees which have been subject to the ravages of the fungus 



Fig. I- — Needleof Doug- 

 las fir infected with 

 the needle-blight fun- 

 gus, showing various 

 forms of apothecia 

 and the manner of 

 their rupture. 



