302 Report of the Botanical Department. 



time the injury occurred. It appears significant also that in instances 

 where trees had been banked with soil the injuries occurred just above 

 the soil while on unbanked trees it usually occurred at the surface 

 of the ground. But this probably does not hold when the ground is 

 not frozen at the time of injury for in that case any bending that may 

 result from strong winds would probably occur at the surface of the 

 ground or even below it, and result in injury at the root crotches. 



Goppert^ maintained that the wind is involved in the production 

 of winter injuries, especially the north wind, for injuries were some- 

 times found confined to plants in certain strips or zones of localities. 

 Excessive evaporation, an additional lowering of the temperature due 

 to wind he believed, were frequently the causes of killing back of 

 shoots and branches of trees. 



Bernbeck^ subjected various plants to wind rates as high as 31.3 

 miles per hour and obtained some very striking results. He found 

 that transpiration was proportional to the wind rate and to the amount 

 of bending or swaying undergone by plant structures, and that the 

 excessive loss of water ceased when bending was eliminated. His 

 results with lignified plant structures are especially pertinent to this 

 discussion. 



A potted plant of Fagus silvatica was exposed to a wind rate of 31.3 

 miles per hour (14 m. per second) and in about 10 days brown spots 

 had developed in the bark, where both the cambium and cortical 

 perenchyma had been killed. Many cell walls are said to have been 

 ruptured. On a potted plant of Picea excelsa exposed to the same 

 wind rate a few hours, the bark on the swaying twigs was cleft open 

 at a number of places on the windward or convex side, exposing the 

 bare wood. Pinus silvestris and P. austriaca sustained similar 

 wounds on the convex sides of twigs when subjected to the same 

 treatment. The clefts closed and became invisible when the normal 

 environment was restored. Ulmus effusa was also injuriously af- 

 fected, but in this case the uninjured areas of bark remained ahve, 

 and after a few weeks the damage done to the woody parts had been 

 practically repaired by growth. 



On a potted specimen of Alnus incana given the same treatment, 

 the bark was injured in many places after several days' exposure. 

 Some injuries occurred also in the wood cylinder but were not evident 

 externally. Knotty masses of callus developed on the injured regions. 

 Quercus pedunculata was similarly affected after 6 days' exposure and 

 also developed knotty enlargements about the old wounds in the 

 course of the summer. Thin lignified twigs of Ulmus effusa, Alnus 

 glutinosa, Fagus silvatica, Picea excelsa, and Larix europaea were ex- 

 posed in duphcate (one set being firmly fixed and the other allowed 



1 L. c. pp. 58-61. 



2 O. Bembeck. Der Wind als pflanzenpathologischer Faktor. 



Inaug. Dissertation, Bonn. p. 116. 1907. 



