184 DISEASES OF THE PINE. 



days and cold niglits, the young pines will snffer the most, and tbey 

 only recover if the soil is not too poor, and the spring and summer are 

 not too dry. Otherwise, large numbers will die, and tbose that survive 

 will be sickly for years, especially if affected in successive years. It has 

 been observed upon newly-planted tracts, that this disease sbows itself 

 only in patches, and that plants sheltered from the midday sun are but 

 slightly, if at all, affected. Pine seed-beds which during the winter and 

 until May were kept covered with lir, spruce, or birch brush were never 

 affected,*while unprotected seed-beds in the immediate neighborhood 

 suffered. If (as is done in the Ellwang forest in Wiirtenberg) fir seeds 

 are sown among the already protected plantations of growing fir plants, 

 they v.ill not be affected. Like results are obtained by an intermixture 

 of pine and spruce, or vice versa. 



Opinions as to the cause. — In regard to the cause of this disease various 

 opinions have been expressed. The origin of the evil has been sought 

 for, as well within the plant itself, as in outward circumstances. 



Many observers believe that the disease starts from the root, and that 

 it is then brought on by root-rust {icurzel rost), root-gangrene [lourzel- 

 Irand), and defective roots, and it has been denominated a gammy or- 

 ganic disease of debility which takes its origin in the root, and by de- 

 grees extends to the leaves. Others ascribe the falling of the leaves to 

 an internal disease — to interruption in the circulation of the sap, the 

 incomplete formation of v/ood in wet seasons, before the setting in of 

 winter — to insects, or to a fungous growth.^ [Ilrjsterium pinastri.) 



The condition of the earth has also been considered as a cause. The 

 disease is favored by a wet sour soil, and especially by a want of strength 

 in the soil. According to some observers, it originates in consequence 

 of clearing, while others ascribe it to a want of light. In the opinion of 

 many, the cause of the disease may be found in the condition of the soil. 

 The majority of foresters, however, adopt the view that its origin is to be 

 ascribed to meteorological conditions, and that it is brought on by very 

 damp unfavorable weather at unusually high temperatures, or by great 

 and sudden changes of temperature in the spring, after cold winters with 

 little snow. The clear nights and late frosts of spring are usually be- 

 lieved to have a bad effect, although it is known that the leaves of the 

 common fir can endure a very low temperature, and that of all the 

 conifercns the pine is found farthest north (04° north latitude). Dr. Nord- 

 linger, of Hohenheim, in his Kritische Blatter (18G3), seeks the origin 

 of this malady in the repeated chilling of the plants, in bare and unpro- 

 tected grounds toward' the end of January, and in February and March. 



Cause of the '■'■ schutV disease explained by the results of forest meteoro- 

 logical observations. — Observations on the temperature of the earth and 

 ground, and a comparison of these records, have led to a new theory as 

 to the cause of this disease. In order, however, to explain the contra- 

 dictory experiences above mentioned, it is necessary to note a few laws 

 .of vegetable physiology that have reference to this subject. 



The leaves of plants impart by evaporation during the growing season 

 a certain amount of watery vapor to the air. The amount of this evap- 

 oration differs, not only in the different kinds of plants, but it also de- 

 pends in the same plants upon external conditions — the temperature of 

 the air, the intensity of light, and on the amount of moisture in the air 

 and in the soil. The greater the warmth of the air, the more intense 

 the solar light, the drier the air, and the moister the soil, by so much 

 more will plants give off" moisture from their leaves, the transpiration 



* So far as known to us, this fungus on pine plants that Lave died from this causo, 

 has not been shown by the microscope, — Ebcrmaijer. 



