688 PROTECTION AGAINST DISEASES. 



is not prevalent in the British Isles. In Germanj' it appears 

 to be connected with the extension of clear-cutting and 

 planting, which, since the end of the eighteenth century, has 

 so largely replaced the system of natural regeneration of the 

 Scots pine. In the damp, cold years 1850 to 1852 needle-cast 

 was widespread and very destructive in North Germany, and 

 again in 1881 to 1884. Pine-plants which have once suffered 

 from it are liable to be again attacked, as they are greatly 

 weakened by the disease. 



4. Causes. 



Numerous reasons have been given for the needle-shedding 

 disease, as quoted by both Von Loffelholz and Holzner. The 

 nature of the soil, the state of the weather, and combinations 

 of these have been cited. Some think that Lophodermium 

 Pinastri is the sole cause of the evil, whilst others hold it to be 

 due to a more rapid transpiration of water by the needles than 

 the roots of the plants can supply. It is therefore probable that 

 we have here to deal with many causes acting in combination, 

 one with another, but these may be reduced to the three 

 following : — 



Needle-cast fungus, Lophodermium Pinastri, Schrad. 



Frosts, and especially early frosts in autumn. 



Insufficient absorption of water to supply that transpired 

 by the plants. 



We have therefore to deal with three forms of the disease: — 



(a) Fungoidal needle-cast. 



(h) Frost needle-cast. 



(c) Dry needle-cast. 



It is difficult to distinguish these causes from one another, 

 as the fungus is always present, though frequently it may be 

 only secondary. 



a. Fum/oidal Keedle-cast. 



The necessary account of this disease has been given above 

 on p. 465. Hartig,* Pranll, and Tursley have supported the 

 fungus theory, but many phenomena appear which con- 

 tradict it, for example, from the disease beginning at the points 



• Vide Hartig, '■ Lehrbuch der Baumkrankheiten.'' Berlin, 2nd edition, 1889, 

 p. 103. 



