1915-16 DEPAETMEx\T OF LANDS, FORESTS AND MINES. 147 



This last season proved to be very unfavourable for the propagation of con- 

 iferous seedlings. The extreme wet weather just after seeding caused coDsider- 

 able loss. This was followed by extreme drought during July and August so that 

 the seedlings have entered the winter in somewhat unfavourable conditions. 



Forest Planting. — The demand for nursery stock for forest planting has fallen 

 off considerably during the past two years. This is probably owing to the labour 

 situation created by war conditions. Last spring we shipped to private owners for 

 demonstration forest jjlanting work, about 150,000 plants. 



White Pine Blister Eust. 



During the past season the Forestry Branch has had charge of the investiga- 

 tion of the " White Pine Blister Eust," which is a plant parasite introduced from 

 Europe during the past decade. 



Description of the Disease. — This disease attacks only the five-leaved pine 

 group, to which our white pine i)eloiigs. Eed or Norway and other two-leaved pines 

 are immune. 



The fungus causing the disease belongs to the rusts, of which the wheat rust is 

 a well-known example. Like the wheat rust, the White Pine Blister Eust has two 

 entirely different hosts. These are the white pine for one stage of growth and 

 currants and gooseberries for the other stage. 



The life history of the blister rust is as follows: The winter spores (seeds) 

 produced during late summer and autumn upon the currant and gooseberry leaves 

 (Figure D) are blown to white pines in the vicinity. They stick to the bark of 

 young trees or branches, germinate, and the young threads penetrate the inner 

 bark tissues. There is no visible sign of the attack for from one to several years, 

 after which a thickening of the region occurs, finally resulting in a more or less 

 spindle-shaped swelling. On this area, early in the spring, blisters appear filled 

 with orange-yellow spores. The blisters break open, setting free the spores inside. 

 This is the most conspicuous stage of the disease on the pine, but lasts only from 

 about the middle of April to the middle of June. (Figure A.) 



The spores (seeds) liberated from the pine blisters are blown about and fall 

 upon the leaves of any currants or gooseberries that may be in the vicinity. Here 

 they germinate at once and infect the leaves. In the course of a couple of weeks 

 a new crop of spores (summer spores) is produced in tiny orange pustules on the 

 lower surface of the currant or gooseberry leaves. (Figure B.) 



These summer spores on being liberated in turn infect other currant and goose- 

 berry leaves, and in another two weeks there is a new crop of summer spores on 

 the new host. (Figure B.) The repetition of this cycle spreads the disease 

 rapidly during the summer in an area which is constantly enlarging. 



Towards the latter part of summer the current and gooseberry leaves produce 

 on their lower surface slender horn-like outgrowths, which give rise to a different 

 kind of spore. (Figure D.) These are known as winter spores and are capable of 

 attacking pines but not currants or gooseberries. 



From this account it is eyident that the two hosts are necessary for this disease 

 to spread. By successive infections of summer spores from diseased currants or 

 gooseberries, this process repeated over and over again during the summer, the- 

 disease may spread long distances, and in the autumn infect white pines by means 

 of the winter spores. These winter spores will attack only the pine. In the 

 following spring the spores produced on pine re-infect the currants and goose- 



