2IO TKANSACTIONS OF ROYAL SCOTTISH AKHORICULTURAL SOCIETY. 



trees grown from seed imported from northern zones were more 

 or less immune from scab infection. Haak's experiments in 

 his scab beds, however, showed that though, for some as yet 

 unexplained reason, plants grown from seeds obtained from the 

 Ural, the north Baltic provinces and Scotland are somewhat 

 less susceptible to infection, none are immune. The choice of 

 seed should therefore be governed by other reasons. 



Haak divides the infections into those brought in from afar, and 

 those caused by diseased leaves in close vicinity of the attacked 

 plants. The spores of Lophoder)iiium are extremely light, form- 

 ing so-called floating spores, and are, in more or less closed forests, 

 carried upwards by ascending air currents and spread to great 

 distances, unless they meet some obstacle to which they adhere 

 at once, thereby causing infection of leaves in the crowns of the 

 trees whenever they find them in a dying condition. Downward 

 air currents carry the few remaining spores to the ground, where 

 they may sometimes settle on young pine growth susceptible to 

 infection. This is the course of infection from afar. That 

 occurring in the vicinity of diseased plants is of practical interest 

 only in nurseries and new cultures, where row upon row of 

 young seedlings or plants occur more or less close together, 

 every leaf being susceptible to infection. Local infection, in 

 destructive intensity, does not extend farther than from 3 to 6 

 feet from the focus, but large quantities of the spores expelled 

 from the cultures may be spread afar, and cause the formation 

 of new centres of the disease. 



It is evident that the first infection of plants in nurseries, unless 

 these are established in the close vicinity of scabic cultures, 

 must be brought from afar. Such infection is rarely intensive 

 during the first year, and can in most cases be checked, so that 

 local centres of the disease are not established. 



The selection of areas for seed nurseries in scab-free localities, 

 either in the open or in forests of deciduous trees, is of the 

 greatest importance. Only places witli the richest soil should 

 be chosen, for the strongest plant has the best chance of escaping 

 the disease or of outgrowing the consequences if attacked. 



The nursery to which the seedlings are to be transplanted 

 should never be close to the sowing .nursery or in the vicinity of 

 pine thickets. When, in jjure pine forests, the selection of places is 

 circumscribed, it is advisable to select localities in mature forests 

 at .some distance from newly cultivated areas or thickets, and 



