INJURIES INDUCED BY PLANTS in 



the pine-leaf cast. Under the name " Pine-blight" (leaf-cast or 

 shedding) the most various diseases have been included. These 

 attack young and old pines, and are characterised by the leaves 

 becoming brown, and usually also by their being prematurely 

 shed. The causes of these diseased conditions are very various. 

 In the first place, frost may actually cause the death of the young 

 leaves of pines. On July 23rd, 1878, large pines, especially such 

 as were growing along the margin of the wood, were so severely 

 affected by frost in the Turoscheln district that those parts of 

 the new leaves which had emerged from the sheath died. 



As however the leaves of the Scotch pine do not protrude from 

 the sheath before the beginning of June, late frost can do injury 

 only in very few cases and in very exceptional localities. In 

 many seasons one observes frequently only on one side, espe- 

 cially the east side, of trees that all the leaves of the youngest 

 shoots on trees that are much exposed to the wind become 

 uniformly brown, except the lowest part, which is enveloped by 

 the sheath. Whether, in such cases, the injury is always due to 

 actual frost, or even to severe cooling, I am not in a position to 

 determine. 



In many cases the browning, death, and shedding of the leaves 

 are the result of drought. 1 In cases where the pine seed-beds 

 have been covered with snow in winter, but which has disappeared 

 after a few warm sunny days without the ground thawing, it will 

 be found that the leaves soon become brown, and that the pines 

 contract " the blight." If one examines the discoloured leaves 

 after the appearance of the first symptoms of the disease, he fre- 

 quently fails to find any trace of mycelia. It is also character- 

 istic that the brownness is equally distributed over the whole 

 leaf, or spreads back from the apex uniformly to a greater or less 

 distance. In such a case we have to do with a drying up of the 

 leaves, which do not receive a sufficient quantity of water from 

 the frozen ground to compensate for the loss by evaporation 

 that takes place in the clear dry weather of winter. Although 

 erroneously ascribed to the action of frost, the cause is the 

 same, too, in cases where the foliage of Pinus Strobus, the spruce, 

 and other conifers, as also dicotyledonous evergreens, becomes 



1 Ebermayer, Die physikalischen Einwirkungen des Waldes auf Luft und 

 Boden, 1873. 



