1905 



FORESTRY AND IRRIGATION 



65 



the effect of the wind was determined 

 at different distances from and to the' 

 leeward of the fields of grass. The 

 counts were made in series along east 

 and west lines at right angles to the 

 margins of the grass fields, and the 

 results are given in the following ta- 

 ble. 



TABLE SHOWING THE DECREASE IN THE NUMBER OF 



YOUNG CLOVER PLANTS PER UNIT AREA WITH 



INCREASE OF DISTANCE TO THE LEEWARD 



OF THE MARGIN OF GRASS LAND. 



Distance No. of No. of No. of 

 from margin Plants. Plants, 

 of grass. 



Feet. 



50 

 200 

 400 



100 



200 

 400 

 600 



800 



IOOO 



400 

 7oo 



Plants. 

 Series i. Series 2. Series 3. 



Field No. i. 



No. of 

 Plants. 

 Total. 



390 

 231 



249 

 277 



i93 



189 



138 



48 



1 130 

 600 

 543 



described, others were made to meas- 

 ure the rate of evaporation at different 

 distances to the leeward of woods, 

 using a form of Piche evaporometer 

 rendered more sensitive by increasing 

 the diameter of the evaporating sur- 

 face to 5.9 inches, thus giving an effec- 

 tive area of 27.06 sq. in., deducting the 

 area of the water reservoir, the latter 

 being graduated to .1, c. c. The in- 

 strument as placed in the field is rep- 

 resented in fig. 4. 



Fig. 4. Showing the form of Piche 

 evaporometer as placed in the field. 



With a series of 6 of these instru- 

 ments set up in a line at right angles 

 to the margin of a black oak grove 

 having a mean height of 12 to 15 feet, 

 the rate of evaporation which occurred 

 simultaneously between 1 1 130 and 

 12:30 A. M. was measured, with the 

 results given in the next table. 



Fig. 4. Showing the form of Piche evaporometer, as 

 placed in the field. 



These three sets of data appear to 

 leave little room to doubt that, in some 

 manner, the grass fields to the wind- 

 ward of the fields seeded to clover did 

 exert an influence which materially 

 affected the stand of clover on them. 

 In what manner this effect may have 

 resulted will be referred to later. 



INFLUENCE OF WOODS UPON THE RATE 

 OF EVAPORATION TO THE LEEWARD. 



At the time of the observations just 



EVAPORATION ONE FOOT ABOVE THE SURFACE AT 



DIFFERENT DISTANCES TO THE LEEWARD OF A 



GROVE OF BLACK OAK IN A FIELD OF SANDY 



SOIL RECENTLY PLANTED TO CORN. 

 Distance from Woods. Evaporation in One Hour. 

 Feet. C. C. 



20 II. O 



40 II. I 



60 II.3 



St> M.2 



TOO i 1-9 



120 12-9 



These results show that until a dis- 

 tance greater than 100 feet is reached 

 but little difference in the rate of evap- 



