MARYLAND WEATHER SERVICE 13 



Wind. — Data on wind velocity are also available only for the Bal- 

 timore station, which may he well taken as representative of the con- 

 ditions as respects this factor for the entire state. The following 

 figures show the total daily wind movement (miles per day) for the 

 different months of the year, being based on the records of the 30 

 years from 1873 to 1902 : 



January, 145; February, 162; March, 175; April, 166; May, 

 149; June, 142; July, 134; August, 122; September, 129; October, 

 137; November, 143; December, 142; Year, 145. 



The most important influence of wind on vegetation lies in its ac- 

 celeration of the rate of transpiration. This is an influence which is 

 exerted upon all the plants of a given region, particularly those 

 which are dominant in the various formations as contrasted with the 

 sheltered subordinate vegetation. As a differential factor influ- 

 encing the occurrence or exclusion of species the wind operates power- 

 fully in situations where the soil moisture content is not high, as on 

 the dunes and on rocky cliffs. Wind influences vegetation in quite 

 another manner, in serving as one of the principal agencies in the 

 distribution of small and buoyant seeds. 



TOPOGRAPHY. 



The topography of an area exerts an influence upon the character 

 and local distribution of plant-life chiefly through its determination 

 of the amount and character of the soil-water, to a less degree through 

 its determination of exposure to insolation and wind. In upland 

 localities away from the influence of streams the water table, or 

 ground water level, is primarily determined by the elevation of the 

 spot under consideration with respect to its immediate surroundings. 

 Tn isolated gravel hills, such as Egg Hill or Foys Hill in Cecil 

 County, the water table is deepest at the summit of the hill but ap- 

 proaches the surface as we descend, and at the base actually reaches 

 the surface in the form of saturated areas of soil or running springs. 

 It is, however, only in hills of homogeneous materials that such a 

 simple condition exists. In hills bearing rock and merely a surface 

 covering of soil the conditions of ground water movement and supply 

 may be complicated in various ways through differences in the per- 



