DISEASES OF THE PINE. 187 



plains and on unprotected grounds, as is so often seen on plant-beds on 

 the south side of forests which were not covered. 



The pine plants are more or less spared from this disease by rainy cloudy 

 weather in the spring, and by being located on northerly slopes, or 

 where protected by a growth of timber, as on the north and west sides 

 of forests, or by artificial protection, or by growing between tall spruce 

 l)lants, or by weeds.^ 



The evaporation of plants is increased in the spring, especially in the 

 month of March, by the extraordinarily dry air which the polar current 

 often brings to us during this month. The disease, therefore, appears 

 oftener in clear, warm spring days, with warm dry air. The reason 

 why pine plants, from five to six years old, are never or but seldom at- 

 tacked by this disease is thus explained : The trunks of the trees form 

 reservoirs of water for the leaves, which supply the loss sustained 

 under the circumstances above described. It is determined from ob- 

 servation that closely-growing plants are more liable to the disease than 

 those growing sparsely. Young plants transplanted will bear the dis- 

 ease better than those raised from seeding. All of these experiences 

 are explained by the more or less complete development of the roots. 

 The greater the number of small fibers in the root (which are the organs 

 for absorption of water), the easier the plant is enabled, even with less 

 activity of the root, in a cold soil, to supply the loss of water by evap- 

 oration, and to withstand a drought. In localities that are too open, 

 the development of the root is imperfect, and care must be taken in 

 the transplanting to use such plants only as have well-developed roots. 



For this same reason with respect to the roots, this disease does not 

 so often aflect plants on strong but loose soils as on those that are poor 

 or very compact, because in loose soils, under circumstances otherwise 

 similar, the development of the roots is more perfect, and their spread 

 greater, than in soils that are more compact. Besides the better devel- 

 opment of the roots, the loosened soil has the advantage of more easily 

 admitting warmth and moisture in the spring. 



By aid of the foregoing explanations, and upon the conclusions fixed 

 by meteorological observations, we may easily explain the causes of the 

 appearance of this disease, under different circumstances. To fix beyond 

 a doubt the correctness of the theories offered in regard to the causes, 

 experimental proofs are only needed, a task which will be undertaken at 

 an early day. 



The means which the forester can apply, to prevent the appearance of 

 this malady, are therefore apparent. All forestal manipulations in trans- 

 planting must tend either to increase the temperature of the earth, in the 

 early months of spring, or to reduce the transpiration ; that is, to weaken 

 the intensity of the light. The former is, however, difficult to attain in 

 large plantations. In seed-beds the radiation of heat can be lessened in 

 some degree by placing a thick covering of moss or leaves between the 

 rows of plants during the winter. In large clearings, if the soil is wet, 

 drainage would improve it; in other soils, loosening as deep as practi- 

 cable, and, according to circumstances, an admixture of humus, will 

 tend greatly to the more ready penetration of warmth into the earth. A 

 lessening of the transpiration can be effected by weakening the light by 

 shading. Seed beds may be protected by evergreen brush, which must 

 not, however, be removed in clear, warm days. Seed-beds should be so 

 located as to be protected on the south side by a forest. In pine reserv- 

 ations on a large scale, the most effectual means of protection will be to 



' If grass or weeds be allovred to grow too high, so as to cover the plants from above, 

 they will destroy them by depriving them of the necessary amount of light. 



