GERMAN NOTES. 207 



and the time during which germs can be expelled is much 

 prolonged. 



Experiments made by Oberforster Haak, in a garden 

 absolutely free from infection, showed that infection could be 

 produced even later than the 15th October, but only in a mild 

 form. This does away with the theory that infection could 

 only take place from July to September. However, cases of 

 infection outside this limit are rare and of relatively a mild 

 character, and for practical purposes in the open it will suffice 

 to combat the pest by syringing the young growth with 

 copper solution from July to September. 



The actual process of infection has been observed to take 

 place in the following manner : — The apothecia on the leaves 

 are disposed in such a manner that the germs can be liberated 

 into the open air. Thus leaves lying fiat on the ground develop 

 apothecia only on the upper surface; those which hang free 

 have them all round. The ripe apothecia open as soon as 

 they have absorbed sufficient moisture from rain or dew, and 

 expel the germs straight into the air to a height of some 3 mm. 

 Air streams convey them farther, but the main infection takes 

 place in close proximity to the centre. Slides placed quite 

 close to leaves bearing open apothecia showed 10,000 to 20,000 

 germs; but on slides at a vertical height of 20 cm. only 12 

 germs could be found ; and on those placed at a slant at 20 cm. 

 distance less than 1000. 



The spores carried away by the wind adhere to the first 

 obstacle they meet so firmly that rain does not wash them 

 away. The germination of the spores begins at once under 

 the influence of sufficient moisture, at any temperature above 

 freezing-point, and the infection of pine leaves with which 

 the spores may have come in contact may take place in a 

 very few days. 



Sulphate of copper in a solution of i to 1000 kills the spores 

 at once, and even one of i to 10,000 prevents their development. 

 Unfortunately the treatment is ineffective as regards i-year- 

 old plants, the leaves of which are coated with a waterproof 

 covering to which the liquid does not adhere. Experiments 

 made by adding soap to the mixture successfully protected the 

 seedlings from the scab infection, but robbed the leaves of 

 their wax covering so that they all died of drought with the 

 first appearance of the spring sun. 



