1907.] 



Pine Disease. 



165 



of its host-plant, but only through a wound made by some 

 other agent. In every diseased shoot examined the presence 

 of one or more slight wounds penetrating the cortex is indicated 

 by a slight incrustation of resin surrounding the injured 

 spot. It is through these injured points that the fungus gains 

 an entrance into the living tissues. When once established, 

 the mycelium extends rapidly towards the tip of the shoot, 

 soon choking up the vessels and arresting the food supply 

 intended for the growing point of the shoot. The mycelium 

 of the fungus does not extend in the shoot for more than one 

 or two inches below the point of infection, consequently 

 the length of a dead shoot depends on the distance below the 

 apex of the wound that enabled the fungus to enter. 



Experiments conducted at Kew show that, within two 

 months after infection, the leaves become yellow and begin 

 to twist, the result of desiccation, and at the expiration of four 

 months all the leaves have fallen, and the shoot is dead. In 

 many other species of Diplodia fruit is not produced on the 

 host-plant until the year following infection, and this condition 

 of things appears to prevail in the fungus under consideration. 

 The fruit condition is indicated by the presence of numerous 

 blackish warts protruding through minute cracks in the 

 dead bark. 



Three-year-old plants of the following species, Weymouth 

 pine (Pinus Strobus, L.), Scots pine (Pinus sylvestris, L.), 

 Spruce (Picea excelsa, L.), Silver Fir (Abies pectinata, DC.) 

 and Larch (Larix europaea, DC.) were infected as follows. 

 Spores obtained from Dr. Somerville's material, and ascertained 

 to be in a condition capable of vigorous germination when 

 placed under favourable conditions, were used. 



Spores placed on the unbroken surface of young shoots 

 failed in every instance to infect the plant, whereas spores 

 placed on the drop of moisture extending from a minute 

 puncture in the bark invariably set up infection, which resulted 

 in the formation of a dense growth of mycelium in the tissues, 

 followed by a yellowing and falling of the leaves, as stated 

 above. 



Positive results were obtained in the case of the two species 

 of Pinus named above. No infection occurred on species of 

 Picea, Abies or Larix. 



