JI4 



DISEASES OF TREES 



south winds. This is to be remembered in instituting preventive 

 measures against the blight. As a rule the diseased leaves of 

 one-year-old seedling-pines die off completely in spring, without 

 however falling off. On the other hand, one finds that all the 



diseased leaves of the bifo- 

 liar spurs of two-year-old 

 pines suddenly become 

 brown after the advent of 

 warmer weather in March 

 or April. This is followed 



FIG. 56. A one-year-old pine in spring which 

 has been attacked by H. rinastri. a, 

 healthy green leaves ; b, leaves with a 

 brown apex and green base ; r, green 

 leaves showing numerous brown blotches ; 

 */, leaves whose upper portion has become 

 brown during the previous winter, and 

 which now bear the spermogonia of H. 

 Pinastri ; the basal portion of these leaves 

 has become brown more recently; , leaves 

 that are completely dead and covered by 

 spermogonia. 



FIG. 57. , a one-year- 

 old pine-leaf in April 

 showing brown spots 

 where infected, but still 

 remaining green to- 

 wards the base ; b, a 

 deadtwo-year-oldpine- 

 leaf in April with 

 ripe perithecia, x, and 

 empty spermogonia, y. 



by a cast that is, by defoliation of the dwarf shoots. This 

 shedding, which frequently follows in a few days, is not to be 

 regarded as the effect of immediately preceding unfavourable 

 climatic conditions. It is, in fact, one result of the formation 

 of cork at the base of the dwarf shoots, which are subsequently 



