82 HATCH EXPEEIMENT STATION. [Jan. 



to this result. It is well known to vegeta])le physiologists 

 that agitation of the leaves of a plant greatly accelerates the 

 process of transpiration, that is to say, the evaporation of 

 water from the leaves. It is also well known that transpira- 

 tion is accelerated by light, a low relative humidity and a 

 high temperature. Such were just the conditions upon May 

 18. * During the months of April and May the rainfall was 

 far below the normal, while the long-continued drouths of 

 the two preceding years will be well remembered. Thus it 

 is evident that the supply of water available to vegetation 

 must have been much less than usual, and under the unusu- 

 ally strong, dry and warm wind of May 18, the leaves of a 

 tree like the maple, with its large leaf surface, might be ex- 

 pected to become greatly exhausted and wilt badly. When 

 this wilting was not carried to excess the leaves recovered ; 

 when, however, it went too far, it resulted in a dying and 

 subsequent shrivelling of the foliage. 



Another factor which must not be overlooked in accounting 

 for this disorder is the maturity of the foliage. Young 

 leaves always give oif the greatest amount of water, and 

 the maple leaves in May are giving off their maximum 

 quantity. 



AVith plenty of water in the soil these high winds would 

 not have caused any wilting ; or, if the same conditions 

 had ensued during August or September, when the foliage 

 was more mature, less wilting would have resulted. The 

 west side of the trees, being the side exposed to the prevail- 

 ing winds, was the most severely affected. 



Top-burn of Lettuce. 

 A disease occurring on greenhouse lettuce, and character- 

 ized as "top-burn" came under our observation the past 

 winter. The disease can readily be distinguished by the 

 withering and subsequent turning back of the tip and margin 

 of the outer leaves, the blackened area sometimes extending 

 inwards an inch or more from the margin. This feature 

 greatly disfigures the plant and consequently affects its 



* Meteorological conditions were as follows : total precipitation, April, 1896, 1 32 

 inches; April, 1895, 5.60 inches; May 1-18, 1896, .16 inch. May 18, maximum 

 velocity of wind 71 miles per hour; relative humidity, 47.31 (average for May, 

 62 5) ; number hours sunshine, 13 (in possible 14^) ; maximum temperature, 84°. 



